Add support for raw VBI capture for the em28xx bridge, currently only for
NTSC.  Support for PAL capture to follow shortly (including the removal of
numerous hard-coded NTSC-specific sizes for capture buffers, etc).

Note that the code currently changes the default current norm from PAL to
NTSC (so that zvbi-ntsc-cc works properly).  The default norm really should
be moved into a board-level parameter.

This work was sponsored by EyeMagnet Limited.
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>