[media] v4l2-core: drop g/s_priority ops

The handling of VIDIOC_G/S_PRIORITY is now entirely done by the V4L2
core, so we can drop the g/s_priority ioctl ops.

We do have to make sure though that when S_PRIORITY is called we check
that the driver used struct v4l2_fh. This check can be removed once all
drivers are converted to that structure.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>