V4L/DVB: cx18: support new vbi ops to set/get VBI format

Also removed the bogus zeroing of fmt.sliced when setting up raw VBI.
This should have been removed in ivtv, but it was just copied-and-pasted
into cx18.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>