V4L/DVB (5977): cx8800: Add register debug functions to radio device too

Add the advanced debug functions to the radio videodev template.  One could
already use them from the video and vbi devices.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>