Rewrite whole af9013 demod driver in order to decrease I2C I/O.

We need to decrease I2C load since AF9015 (I2C adapter / USB-bridge used)
seems to have some problems under heavy I2C traffic.
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>