[test] Move pr73894.ll to AArch64 directory and update the target triple (#84269)

pr73894.ll is failing on a number of non-AArch64 buildbots. I'm not
certain that this is a proper fix, but I think it's best to move the
test to the test/Transforms/LoopVectorize/AArch64/ directory and replace
the triple with one commonly used in that directory.

#73894

Author: mcinally

llvm/test/Transforms/LoopVectorize/pr73894.ll renamed to llvm/test/Transforms/LoopVectorize/AArch64/pr73894.ll

@@ -1,7 +1,7 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
 ; RUN: opt -passes=loop-vectorize -mcpu=neoverse-v1 -force-vector-interleave=2 -force-vector-width=1 -S %s | FileCheck %s
 
-target triple = "arm64-linux"
+target triple = "aarch64-unknown-linux-gnu"
 
 define i32 @pr70988() {
 ; CHECK-LABEL: define i32 @pr70988(