intel/cs: Push subgroup ID instead of base thread ID

We're going to want subgroup ID for SPIR-V subgroups eventually anyway.
We really only want to push one and calculate the other from it.  It
makes a bit more sense to push the subgroup ID because it's simpler to
calculate and because it's a real API thing.  The only advantage to
pushing the base thread ID is to avoid a single SHL in the shader.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

src/intel/compiler/brw_nir.h

@@ -95,7 +95,8 @@ void brw_nir_analyze_boolean_resolves(nir_shader *nir);
 nir_shader *brw_preprocess_nir(const struct brw_compiler *compiler,
                                nir_shader *nir);
 
-bool brw_nir_lower_cs_intrinsics(nir_shader *nir);
+bool brw_nir_lower_cs_intrinsics(nir_shader *nir,
+                                 unsigned dispatch_width);
 void brw_nir_lower_vs_inputs(nir_shader *nir,
                              bool use_legacy_snorm_formula,
                              const uint8_t *vs_attrib_wa_flags);