[media] videodev.h: add V4L2_CTRL_FLAG_MODIFY_LAYOUT

Add new flag to indicate that changing this control will change the
buffer/mediabus layout as well.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>