spirv: Implement SPV_KHR_shader_clock

We only have the subgroup variant in NIR (equivalent to clockARB), so
only support that for now.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/compiler/shader_info.h

@@ -60,6 +60,7 @@ struct spirv_supported_capabilities {
    bool post_depth_coverage;
    bool runtime_descriptor_array;
    bool float_controls;
+   bool shader_clock;
    bool shader_viewport_index_layer;
    bool stencil_export;
    bool storage_8bit;