Add MPEG 4 codec

This patch introduces the support of MPEG4 video decoding. It basically
just copies data from VA's frame/slice headers data structures to v4l's
MPEG4 frame header extended controls data structures.

src/context.h

@@ -52,6 +52,7 @@ struct object_context {
 	uint32_t num_rendered_surfaces;
 
 	struct v4l2_ctrl_mpeg2_frame_hdr mpeg2_frame_hdr;
+	struct v4l2_ctrl_mpeg4_frame_hdr mpeg4_frame_hdr;
 };
 
 typedef struct object_context *object_context_p;