[media] v4l: v4l2_subdev pad-level operations

Add a v4l2_subdev_pad_ops structure for the operations that need to be
performed at the pad level such as format-related operations.

Pad format-related operations use v4l2_mbus_framefmt instead of
v4l2_format.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/v4l2-subdev.h

@@ -413,6 +413,9 @@ struct v4l2_subdev_ir_ops {
 				struct v4l2_subdev_ir_parameters *params);
 };
 
+struct v4l2_subdev_pad_ops {
+};
+
 struct v4l2_subdev_ops {
 	const struct v4l2_subdev_core_ops	*core;
 	const struct v4l2_subdev_tuner_ops	*tuner;
@@ -421,6 +424,7 @@ struct v4l2_subdev_ops {
 	const struct v4l2_subdev_vbi_ops	*vbi;
 	const struct v4l2_subdev_ir_ops		*ir;
 	const struct v4l2_subdev_sensor_ops	*sensor;
+	const struct v4l2_subdev_pad_ops	*pad;
 };
 
 /*