glsl_to_tgsi: reduce the size of glsl_to_tgsi_instruction using bitfields
glsl_to_tgsi: reduce the size of glsl_to_tgsi_instruction using bitfields

sizeof(glsl_to_tgsi_instruction): 464 -> 416

Reviewed-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>
Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler