[AMDGPU] SDWA: make pass global

Summary: Remove checks for basic blocks.

Reviewers: vpykhtin, rampitec, arsenm

Subscribers: kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye

Differential Revision: https://reviews.llvm.org/D31935

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300040 91177308-0d34-0410-b5e6-96231b3b80d8