[AMDGPU] Enable compare operations to be selected by divergence

Summary: Details: This patch enables SETCC to be selected to S_CMP_* if uniform and V_CMP_* if divergent.

Reviewers: rampitec, arsenm

Reviewed By: rampitec

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82194