R600/SI: Rewrite VOP1InstSI to contain a pseudo and _si opcode

What this does is that if you accidentally select these instructions on VI,
the code generation will fail, because the pseudo -> _vi mapping will be
undefined.

The idea is to be able to catch possible future bugs easily.

Tested-by: Michel Dänzer <michel.daenzer@amd.com>
llvm-svn: 228038