[media] mn88472: convert driver to I2C client

It uses I2C bus so better to implement it as a standard I2C driver
model. It was using proprietary DVB binding.

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