[media] it913x: fix tuner sleep power leak

IT913x tuner driver disables own clock, provided by demod core, as
very a first operation when tuner is put on *sleep*. That likely
causes failure of all the rest commands on sleep sequence, which
leads situation where tuner is not actually on sleep, but consuming
a lot of power.

I measured 102mA current consumption from the USB before change
and after change it was only 32mA. Used device was single tuner
IT9135 BX.

Second reason to remove that register from tuner driver is reason
it is simply on wrong driver (demod vs. tuner), breaking the
principle of correct driver.

Clock is now provided more correctly af9033 demod driver as a
config option.

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