V4L/DVB (6447): tuner: add i2c_gate_ctrl function to struct analog_tuner_ops

V4L/DVB (6447): tuner: add i2c_gate_ctrl function to struct analog_tuner_ops

In some designs, the tuner silicon may be on an i2c bus behind an i2c gate,
controlled by the analog demodulator.  We already have a method to control
such i2c gates when they are controlled by the digital demodulator, but in
some hybrid designs, there may be an i2c gate controlled by each demodulator.

For example, when in analog tuning mode, one would access the tuner by opening
the i2c gate controlled by the analog demodulator, while when in digital
tuning mode, one would access the tuner by opening the i2c gate controlled by
the digital demodulator.

We must add this callback function to analog_tuner_ops in order to handle
such configurations.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>