[AMDGPU][MC] Fix for Bug 28158 + LIT tests

Added support of the following instructions:
- s_cbranch_cdbgsys
- s_cbranch_cdbgsys_and_user
- s_cbranch_cdbgsys_or_user
- s_cbranch_cdbguser
- s_setkill

Reviewers: vpykhtin

Differential Revision: https://reviews.llvm.org/D31469

llvm-svn: 299567