[media] si2168: avoid firmware loading if it has been loaded previously

Add a variable to keep track if firmware is loaded or not and skip parts of the
initialization if fw is already loaded. Resume from sleep with a different
command compared to initial power up and run command 85 after resume command.
This behaviour is observed when using manufacturer provided binary-only si2168
driver for TechnoTrend CT2-4400.

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