[AMDGPU] Assembler: support SDWA and DPP for VOP2b instructions

Reviewers: nhaustov, artem.tamazov, vpykhtin, tstellarAMD

Subscribers: arsenm, kzhuravl, wdng, nhaehnle, yaxunl, tony-tye

Differential Revision: https://reviews.llvm.org/D28051

llvm-svn: 290599