media: omap3isp: Explicitly set the number of CSI-2 lanes used in lane cfg

The omap3isp driver extracts the CSI-2 lane configuration from the V4L2
fwnode endpoint but misses the number of lanes itself. Get this information
and use it in PHY configuration.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>