AMDGPU: Add support for 's' and 'v' asm constraints

Summary: 's' is used to specify sgprs and 'v' is used to specify vgprs.

Reviewers: arsenm, echristo

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D14307

llvm-svn: 253610
2 files changed