e4000: convert DVB tuner to I2C driver model

Driver conversion from proprietary DVB tuner model to more
general I2C driver model.

Cc: Jean Delvare <khali@linux-fr.org>
Cc: Mauro Carvalho Chehab <m.chehab@samsung.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
e4000: add manual gain controls

Add gain control for LNA, Mixer and IF. Expose controls via DVB
frontend .set_config callback.

Signed-off-by: Antti Palosaari <crope@iki.fi>
rtl2832_sdr: expose E4000 gain controls to user space

Provide E4000 gain controls to userspace via V4L2 API. LNA, Mixer
and IF gain controls are offered, each one both manual and automode.

Signed-off-by: Antti Palosaari <crope@iki.fi>
r820t: add manual gain controls

Add gain control for LNA, Mixer and IF. Expose controls via DVB
frontend .set_config callback.

Signed-off-by: Antti Palosaari <crope@iki.fi>
rtl2832_sdr: expose R820 gain controls to user space

Provide R820 gain controls to userspace via V4L2 API. LNA, Mixer
and IF gain controls are offered, each one both manual and automode.

Signed-off-by: Antti Palosaari <crope@iki.fi>