V4L/DVB (8956): bttv: Turn video_nr, vbi_nr and radio_nr into arrays

With video_nr, vbi_nr and radio_nr being simple integers, it is not
possible to use these parameters on a system with multiple bttv
adapters (which happens to be my case.) video_register_device() will
always fail on the second and later adapters. Turn these parameters
into arrays, as many other V4L drivers are already doing, so that they
can be used on such systems.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>