V4L/DVB (5610): M920x: remove duplicated code

Some of the devices supported by the m920x driver have identical functions used
for tuner_attach and frontend_attach.  This patch consolidates the functions in
question, and updates the debug code to be generic for each.  This patch
decreases the size of the kernel.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>