Add example script to run on cpu

Summary: An example script to build and run executor_runner baremetal version on ARM M-class CPUs

```
I executorch:runner.cpp:63] Model PTE file loaded. Size: 960 bytes.
I executorch:runner.cpp:69] Model buffer loaded, has 1 methods
I executorch:runner.cpp:77] Running method forward
I executorch:runner.cpp:94] Setting up planned buffer 0, size 32.
I executorch:runner.cpp:109] Method loaded.
I executorch:runner.cpp:111] Preparing inputs...
I executorch:runner.cpp:113] Input prepared.
I executorch:runner.cpp:115] Starting the model execution...
I executorch:runner.cpp:120] Model executed successfully.
I executorch:runner.cpp:124] 1 outputs:
Output[0][0]: 0.500000
Output[0][1]: 0.500000
Output[0][2]: 0.500000
Output[0][3]: 0.500000
```

Differential Revision: D49900956

fbshipit-source-id: e30571f95abd5311f3ab649fcb1d154b4f5c3310

Author: digantdesai

examples/backend/arm/run.sh

@@ -0,0 +1,123 @@
+#!/usr/bin/env bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -eu
+
+########
+### Hardcoded constants
+########
+script_dir=$(cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd)
+et_root_dir=$(readlink -f ${script_dir}/../../../)
+et_build_dir=${et_root_dir}/cmake-out
+ethos_u_root_dir=${1:-"$(readlink -f ${script_dir}/../ethos-u)"}
+ethos_u_build_dir=${ethos_u_root_dir}/core_platform/build
+fvp_model=FVP_Corstone_SSE-300_Ethos-U55
+toolchain_cmake=${ethos_u_root_dir}/core_platform/cmake/toolchain/arm-none-eabi-gcc.cmake
+_setup_msg="please refer to ${script_dir}/ethos-u-setup/setup.sh to properly install necessary tools."
+
+
+# Generate eager mode results
+# TODO
+
+# Generate the PTE file
+function generate_pte_file() {
+    cd $et_root_dir
+    python3 -m examples.export.export_example --model_name="softmax"
+    local pte_file=$(readlink -f ./softmax.pte)
+    [[ -f ${pte_file} ]] || { echo "Failed to generate a pte file - ${pte_file}"; exit 1; }
+    echo "${pte_file}"
+}
+
+# build ExecuTorch Libraries
+function build_executorch() {
+    mkdir "${et_build_dir}"
+    cd "${et_build_dir}"
+    cmake                                           \
+        -DBUCK2=/tmp/buck2                          \
+        -DEXECUTORCH_BUILD_XNNPACK=OFF              \
+        -DFLATC_EXECUTABLE="$(which flatc)"         \
+        -DCMAKE_TOOLCHAIN_FILE="${toolchain_cmake}" \
+        -DEXECUTORCH_BUILD_HOST_TARGETS=OFF         \
+        -DCMAKE_BUILD_TYPE=Release                  \
+        -DEXECUTORCH_ENABLE_LOGGING_RELEASE_MODE=ON \
+        -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=OFF      \
+        -DEXECUTORCH_BUILD_GFLAGS=OFF               \
+        -DSELECT_OPS_LIST="aten::_softmax.out"      \
+        "${et_root_dir}"
+
+    echo "[${FUNCNAME[0]}] Configured CMAKE"
+
+    n=$(nproc)
+    cmake --build . -j"$((n - 5))"
+    echo "[${FUNCNAME[0]}] Generated static libraries for ExecuTorch:"
+    find . -name "*.a" -exec ls -al {} \;
+}
+
+# build Arm Baremetal executor_runner
+function build_executorch_runner() {
+    [[ $# -ne 1 ]] && { echo "[${FUNCNAME[0]}] Expecting pte file as an argument got, $@"; exit 1; }
+    local pte=${1}
+    cd "${ethos_u_root_dir}"/core_platform
+    cmake                                         \
+        -DCMAKE_TOOLCHAIN_FILE=${toolchain_cmake} \
+        -B build targets/corstone-300             \
+        -DET_DIR_PATH:PATH=${et_root_dir}         \
+        -DET_BUILD_DIR_PATH:PATH=${et_build_dir}  \
+        -DET_PTE_FILE_PATH:PATH="${pte}"          \
+        -DPYTHON_EXECUTABLE=$(which python3)
+    echo "[${FUNCNAME[0]}] Configured CMAKE"
+
+    n=$(nproc)
+    cmake --build build -- -j"$((n - 5))" executor_runner VERBOSE=1
+    echo "[${FUNCNAME[0]}] Generated baremetal elf file:"
+    find . -name "executor_runner.elf"
+}
+
+# Execute the executor_runner on FVP Simulator
+function run_fvp() {
+    elf=$(find ${ethos_u_build_dir} -name "executor_runner.elf")
+    [[ ! -f $elf ]] && { echo "[${FUNCNAME[0]}]: Unable to find executor_runner elf: ${elf}"; exit 1; }
+    FVP_Corstone_SSE-300_Ethos-U55                          \
+        -C ethosu.num_macs=128                              \
+        -C mps3_board.visualisation.disable-visualisation=1 \
+        -C mps3_board.telnetterminal0.start_telnet=0        \
+        -C mps3_board.uart0.out_file='-'                    \
+        -a "${elf}"                                         \
+        --timelimit 30 # seconds
+    echo "[${FUNCNAME[0]} Simulation complete, $?"
+}
+
+#######
+### Main
+#######
+
+# basic checks before we get started
+hash ${fvp_model} \
+    || { echo "Could not find ${fvp_model} on PATH, ${_setup_msg}"; exit 1; }
+
+hash arm-none-eabi-gcc \
+    || { echo "Could not find arm baremetal toolchain on PATH, ${_setup_msg}"; exit 1; }
+
+[[ -f ${toolchain_cmake} ]] \
+    || { echo "Could not find ${toolchain_cmake} file, ${_setup_msg}"; exit 1; }
+
+[[ -f ${et_root_dir}/CMakeLists.txt ]] \
+    || { echo "Executorch repo doesn't contain CMakeLists.txt file at root level"; exit 1; }
+
+# get the pte
+pte=$(generate_pte_file)
+
+# build et
+build_executorch
+
+# build the et baremetal app
+build_executorch_runner "${pte}"
+
+# run the app
+run_fvp
+
+exit $?