cx18: convert driver to use video_ioctl2().  Pushed down ioctl debug
messages and priority checks as well.  Still left serialization lock in
place for now.  #if 0'ed out sliced vbi ioctl code for now.

Patch heavily based on similar changes made to ivtv by Hans Verkuil.
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>