[AMDGPU][MC] Added support of 256- and 512-bit tuples of ttmp registers

See bug 35561: https://bugs.llvm.org/show_bug.cgi?id=35561

This patch also affects implementation of SGPR and VGPR registers though changes are cosmetic.

Reviewers: artem.tamazov, arsenm

Differential Revision: https://reviews.llvm.org/D41437

llvm-svn: 321359