[media] cx23885: add i2c client handling into dvb_unregister and state

Prepare cx23885 driver for handling I2C client that is needed for certain demodulators and tuners (for example Si2168 and Si2157). I2C client for tuner and demod stored in state and unregistering of the I2C devices added into dvb_unregister.

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