intel/fs: fix subgroup invocation read bounds checking

nir->info.subgroup_size can be set to an enum :
  SUBGROUP_SIZE_VARYING = 0
  SUBGROUP_SIZE_UNIFORM = 1
  SUBGROUP_SIZE_API_CONSTANT = 2
  SUBGROUP_SIZE_FULL_SUBGROUPS = 3

So compute the API subgroup size value and compare it to the dispatch
size to determine whether we need some bound checking.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 9ac192d79d ("intel/fs: bound subgroup invocation read to dispatch size")
Reviewed-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21856>

src/intel/compiler/brw_nir.h

@@ -160,6 +160,9 @@ void brw_nir_apply_key(nir_shader *nir,
                        unsigned max_subgroup_size,
                        bool is_scalar);
 
+unsigned brw_nir_api_subgroup_size(const nir_shader *nir,
+                                   unsigned hw_subgroup_size);
+
 enum brw_conditional_mod brw_cmod_for_nir_comparison(nir_op op);
 enum lsc_opcode lsc_aop_for_nir_intrinsic(const nir_intrinsic_instr *atomic);
 enum brw_reg_type brw_type_for_nir_type(const struct intel_device_info *devinfo,