media: v4l: omap3isp: Get the parallel bus type from DT

The OMAP3 ISP supports both external and embedded BT.656 synchronization
for parallel buses. It currently gets the bus type information from the
source subdev through the .g_mbus_config() operation, but should instead
get it from DT as that's the authoritative source of bus configuration
information.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>