[media] si2168: add support for 1.7MHz bandwidth

This patch is based on Antti's silabs branch.

Add support for 1.7 MHz bandwidth. Supported in all versions of Si2168 according to short data sheets.

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