intel/compiler: Be more conservative about subgroup sizes in GL

The rules for gl_SubgroupSize in Vulkan require that it be a constant
that can be queried through the API.  However, all GL requires is that
it's a uniform.  Instead of always claiming that the subgroup size in
the shader is 32 in GL like we have to do for Vulkan, claim 8 for
geometry stages, the maximum for fragment shaders, and the actual size
for compute.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/intel/compiler/brw_nir.h

@@ -140,6 +140,7 @@ void brw_nir_apply_tcs_quads_workaround(nir_shader *nir);
 void brw_nir_apply_key(nir_shader *nir,
                        const struct brw_compiler *compiler,
                        const struct brw_base_prog_key *key,
+                       unsigned max_subgroup_size,
                        bool is_scalar);
 
 enum brw_reg_type brw_type_for_nir_type(const struct gen_device_info *devinfo,