spirv: add interface for drivers to define support extensions.

I expect over time the struct contents will change as all
drivers support stuff etc, but for now this should be a good
starting point.

Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/intel/vulkan/anv_pipeline.c

@@ -124,7 +124,7 @@ anv_shader_compile_to_nir(struct anv_device *device,
    nir_function *entry_point =
       spirv_to_nir(spirv, module->size / 4,
                    spec_entries, num_spec_entries,
-                   stage, entrypoint_name, nir_options);
+                   stage, entrypoint_name, NULL, nir_options);
    nir_shader *nir = entry_point->shader;
    assert(nir->stage == stage);
    nir_validate_shader(nir);