[AMDGPU] gfx10 atomic optimizer changes.

Summary:
Add support for gfx10, where all DPP operations are confined to work
within a single row of 16 lanes, and wave32.

Reviewers: arsenm, sheredom, critson, rampitec

Subscribers: kzhuravl, jvesely, wdng, nhaehnle, yaxunl, t-tye, hiraditya, jfb, dstuttard, tpr, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65644

llvm-svn: 369745