[media] si2168: add support for gapped clock

Add a parameter in si2168_config to support gapped clock. This might be
necessary on some devices with higher bitrates.

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>