[AMDGPU][MC][GFX9] Added s_scratch* instructions

See bug 36836: https://bugs.llvm.org/show_bug.cgi?id=36836

Differential Revision: https://reviews.llvm.org/D44832

Reviewers: artem.tamazov, arsenm, timcorringham

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328704 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed