media: i2c: ov772x: Add support for BT.656 mode

Add support to read the bus-type for V4L2_MBUS_BT656 and enable BT.656
mode in the sensor if needed.

For backward compatibility with older DTS where the bus-type property was
not mandatory, assume V4L2_MBUS_PARALLEL as it was the only supported bus
at the time. v4l2_fwnode_endpoint_alloc_parse() will not fail if
'bus-type' is not specified.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>