[AMDGPU] AsmParser: disable DPP for unsupported instructions. New dpp tests. Fix v_nop_dpp.

Summary:
1. Disable DPP encoding for instructions that do not support it:
    - VOP1:
        - v_readfirstlane_b32
        - v_clrexcp
        - v_movreld_b32
        - v_movrels_b32
        - v_movrelsd_b32
    - VOP2:
        - v_madmk_f16/32
        - v_madak_f16/32
    - VOPC, VINTRP, VOP3
2. Fix DPP for v_nop
3. New DPP tests for VOP1 and VOP2 instructions

Reviewers: nhaustov, tstellarAMD, vpykhtin

Subscribers: tstellarAMD, arsenm

Differential Revision: http://reviews.llvm.org/D18552

llvm-svn: 265538