[AMDGPU] Move WQM/WWM intrinsic instruction selection to AMDGPUISelDAGToDAG

Reviewers: arsenm, nhaehnle

Reviewed By: arsenm

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65328

llvm-svn: 367105