[media] rtl2832: add code to bind r820t on it

There are some init stuff to be done for each new tuner at the
demod code. Add the code there for r820t.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: Antti Palosaari <crope@iki.fi>