[media] v4l: Aptina-style sensor PLL support

Add a generic helper function to compute PLL parameters for PLL found in
several Aptina sensors.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>