Add device tree binding documentation for the OV2680 camera sensor.

[Sakari Ailus: Squash MAINTAINERS entry from Rui]

CC: devicetree@vger.kernel.org
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>