V4L/DVB (8063): cx18: Fix unintended auto configurations in cx18-av-core

Change the cx18-av-core code so that accesses to cx23418 av core that
cause auto-configuration will be adjusted to emulate the auto-configuration
behavior of the cx25843.  This fixes the VBI displayed as video at the top of
the frame for NTSC and probably other things.

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