drm/bridge: ti-tfp410: Set the bus_format

The TFP410 supports 24 bit, single-edge and 12 bit, dual-edge modes.
Depending on how many wires are used (24/12) the driver can set the correct
bus_format.

If the information is not available in DT then assume 24 bit, single-edge
setup.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190401124143.17179-3-peter.ujfalusi@ti.com