[media] rtl28xxu: add support for Panasonic MN88473 slave demod

There is RTL2832P devices having extra MN88473 demodulator. This
patch add support for such configuration. Logically MN88473 slave
demodulator is connected to RTL2832 master demodulator, both I2C
bus and TS input. RTL2832 is integrated to RTL2832U and RTL2832P
chips. Chip version RTL2832P has extra TS interface for connecting
slave demodulator.

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