[media] rtl28xxu: add heuristic to detect chip type

Detect automatically whether chip is old RTL2831U or newer
RTL2832U/RTL2832P. Detection is based I2C command that is found only
from newer RTL2832U models.

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