AMDGPU: Lower buffer store and atomic intrinsics manually

Summary:
Without this, SIMemoryLegalizer inserts s_waitcnt vmcnt(0) before every
buffer store and atomic instruction.

Reviewers: arsenm, nhaehnle

Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, llvm-commits, t-tye

Differential Revision: https://reviews.llvm.org/D39060

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317754 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed