[media] fc2580: implement V4L2 subdevice for SDR control

Implement V4L2 subdevice for bandwidth and frequency controls of
SDR usage. That driver now implements both DVB frontend and V4L2
subdevice. Driver itself is I2C driver. Lets see how it works.

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