[media] rtl2830: implement own I2C locking

Own I2C locking is needed due to two special reasons:
1) Chips uses multiple register pages/banks on single I2C slave.
Page is changed via I2C register access.
2) Chip offers muxed/gated I2C adapter for tuner. Gate/mux is
controlled by I2C register access.

Due to these reasons, I2C locking did not fit very well.

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