r600g,radeonsi: convert TGSI shader type to LLVM shader type

r600g,radeonsi: convert TGSI shader type to LLVM shader type

The values are hardcoded in the LLVM backend, but the TGSI definitions are
going to be changed with tessellation, e.g. TGSI_PROCESSOR_COMPUTE will be
increased by 2.

We'll use VS for LS and HS, because there's nothing special about them
from the LLVM backend point of view, even though the hardware side is
different. We do the same for ES.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>