AMDGPU: Relax 32-bit SGPR register class

Mostly use SReg_32 instead of SReg_32_XM0 for arbitrary values. This
will allow the register coalescer to do a better job eliminating
copies to m0.

For GlobalISel, as a terrible hack, use SGPR_32 for things that should
use SCC until booleans are solved.

git-svn-id: 91177308-0d34-0410-b5e6-96231b3b80d8
104 files changed