[AMDGPU] Assembler: match e32 VOP instructions before e64.

Summary:
Split assembler match table in 4 tables with assembler variants:

Default - all instructions except VOP3, SDWA and DPP
  - VOP3
  - SDWA
  - DPP
First match Default table then VOP3, SDWA and DPP.

Reviewers:  tstellarAMD, artem.tamazov, vpykhtin

Subscribers: arsenm, wdng, nhaehnle, AMDGPU

Differential Revision: https://reviews.llvm.org/D24252

llvm-svn: 281023