V4L/DVB (6332): cx88: Only include the blackbird fields if blackbird is selected

Add some ifdefs around fields only used for blackbird support, similar to the
way the dvb fields are only included with dvb support.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Reviewed-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>