[media] media: New flag V4L2_CTRL_FLAG_EXECUTE_ON_WRITE

Create a new flag that represent controls which its value needs to be
passed to the driver even if it has not changed.

They typically represent actions, like triggering a flash or clearing an
error flag. So writing to such a control means some action is executed.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>