[CodeGen] Add machine verification to a couple of tests

This helps to provoke a couple of errors when I apply D129208 that would
otherwise only show up in an LLVM_ENABLE_EXPENSIVE_CHECKS build.

Author: jayfoad

llvm/test/CodeGen/AArch64/regcoal-physreg.mir

@@ -1,4 +1,4 @@
-# RUN: llc -mtriple=aarch64-apple-ios -run-pass=simple-register-coalescing %s -o - | FileCheck %s
+# RUN: llc -mtriple=aarch64-apple-ios -run-pass=simple-register-coalescing -verify-machineinstrs %s -o - | FileCheck %s
 --- |
   declare void @f2()
 

llvm/test/CodeGen/AMDGPU/subreg-intervals.mir

@@ -1,4 +1,4 @@
-# RUN: llc -march=amdgcn -run-pass liveintervals -debug-only=regalloc -o /dev/null %s 2>&1 | FileCheck %s
+# RUN: llc -march=amdgcn -run-pass liveintervals -debug-only=regalloc -verify-machineinstrs -o /dev/null %s 2>&1 | FileCheck %s
 # REQUIRES: asserts
 
 # CHECK: INTERVALS