nir/spirv: Add support for device groups

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>

src/compiler/shader_enums.h

@@ -558,6 +558,9 @@ typedef enum
    SYSTEM_VALUE_LOCAL_GROUP_SIZE,
    /*@}*/
 
+   /** Required for VK_KHR_device_group */
+   SYSTEM_VALUE_DEVICE_INDEX,
+
    /** Required for VK_KHX_multiview */
    SYSTEM_VALUE_VIEW_INDEX,