anv,intel: Enable nir_opt_large_constants for Vulkan

According to RenderDoc, this shaves 99.6% of the run time off of the
ambient occlusion pass in Skyrim Special Edition when running under DXVK
and shaves 92% off the runtime for a reasonably representative frame.
When running the actual game, Skyrim goes from being a slide-show to a
very stable and playable framerate on my SKL GT4e machine.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/compiler/brw_compiler.h

@@ -112,6 +112,12 @@ struct brw_compiler {
     * will attempt to push everything.
     */
    bool supports_pull_constants;
+
+   /**
+    * Whether or not the driver supports NIR shader constants.  This controls
+    * whether nir_opt_large_constants will be run.
+    */
+   bool supports_shader_constants;
 };
 
 /**