glsl_to_tgsi: reduce the size of glsl_to_tgsi_instruction using bitfields

sizeof(glsl_to_tgsi_instruction): 464 -> 416

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
1 file changed