Sparc: Add the "alternate address space" load/store instructions.

- Adds support for the asm syntax, which has an immediate integer
  "ASI" (address space identifier) appearing after an address, before
  a comma.

- Adds the various-width load, store, and swap in alternate address
  space instructions. (ldsba, ldsha, lduba, lduha, lda, stba, stha,
  sta, swapa)

This does not attempt to hook these instructions up to pointer address
spaces in LLVM, although that would probably be a reasonable thing to
do in the future.

Differential Revision: http://reviews.llvm.org/D8904

llvm-svn: 237581