R600/SI: Rework MUBUF store instructions

The lowering of stores is now mostly handled in the tablegen files.  No
more BUFFER_STORE nodes I generated during legalization.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183130 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed