[AMDGPU] set read_only access qualifier for pointers

If a kernel's pointer argument is known to be readonly
set access qualifier accordingly. This allows RT not to
flush caches before dispatches.

Differential Revision: https://reviews.llvm.org/D32091

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300362 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed