V4L/DVB (11864): cx18: Complete support for Sliced and Raw VBI for 625 line systems

Finish changes for sliced and raw VBI for 625 line systems.  Tested with VPS
and WSS being emitted by a PVR-350 in field 1 lines 16 and 23.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>