gallium/pipe: Add get_resources() to pipe_video_buffer

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23159>

src/gallium/include/pipe/p_video_codec.h

@@ -181,6 +181,12 @@ struct pipe_video_buffer
     */
    void (*destroy)(struct pipe_video_buffer *buffer);
 
+   /**
+    * get an individual resource for each plane,
+    * only returns existing resources by reference
+    */
+   void (*get_resources)(struct pipe_video_buffer *buffer, struct pipe_resource **resources);
+
    /**
     * get an individual sampler view for each plane
     */