i965/gen6/gs: Implement GS_OPCODE_SET_PRIMITIVE_ID.

i965/gen6/gs: Implement GS_OPCODE_SET_PRIMITIVE_ID.

In gen6 the geometry shader payload includes the PrimitiveID information in
r0.1. When the shader code uses glPimitiveIdIn we will have to move this to
a separate hardware register where we can map this attribute. This opcode
takes the selected destination register and moves r0.1 there.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>