[media] cx23885: implement num_fds_portb, num_fds_portc parameters for cx23885_board structure

This is needed for multifrontend support.
NetUP Dual DVB-T/C CI RF card has frontends connected to port B & C
Each frontend has two switchable cores - DVB-T & DVB-C

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