[media] cx23885: implement tuner_bus parameter for cx23885_board structure

There is two external I2C buses in cx23885 chip.
Currently, analog tuners supported for second I2C bus only
In NetUP Dual DVB-T/C CI RF card tuners connected to first bus
So, in order to support analog tuners sitting on first bus
we need modifications.

Signed-off-by: Igor M. Liplianin <liplianin@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>