AMDGPU: Add volatile to test loads and stores

When the memory vectorizer is enabled, these tests break.
These tests don't really care about the memory instructions,
and it's easier to write check lines with the unmerged loads.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266071 91177308-0d34-0410-b5e6-96231b3b80d8
19 files changed