media: dt-bindings: media: Add bindings for OV2685

Add device tree binding documentation for the OV2685 sensor.

Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.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@s-opensource.com>