AMDGPU: Cleanup. Use definesRegister instead of manual loop

Also this will be more precise since it will check
exec_lo/exec_hi writes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274817 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed