[media] cx231xx: Make the DIF configuration based on the tuner not the board id

The current code was deciding whether a DIF was present based on the board
profile.  However, this is just another thing for someone to get wrong when
adding new boards.  Make the decision based on the tuner instead, so that a
developer adding new boards only needs to specify which tuner the device has.

Of course, the first time somebody adds a board with a tuner other than xc5000
or tda18271, he/she will need to add another line for that tuner.  But we
provide a friendly message in dmesg to let them know that.

Signed-off-by: Devin Heitmueller <dheitmueller@hauppauge.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>