R600/SI: Make fitsRegClass() operands const

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
R600/SI: Use the same names for VOP3 operands and encoding fields

This makes it possible to reorder the operands without breaking the
encoding.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
R600/SI: Add patterns for 64-bit shift operations

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
R600: Swap the legality of rotl and rotr

The hardware supports rotr and not rotl.
R600/SI: Add pattern for rotr

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
R600/SI: Add a pattern for S_LOAD_DWORDX2_* instructions

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
R600/SI: Use a multiclass for MUBUF_Load_Helper

This will simplify the instructions and also the pattern definitions.

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