media: dt-bindings: media: Define "rotation" property for sensors

Sensors are occasionally mounted upside down to systems such as mobile
phones or tablets. In order to use such a sensor without having to turn
every image upside down, most camera sensors support reversing the readout
order by setting both horizontal and vertical flipping.

This patch documents the "rotation" property for camera sensors, mirroring
what is defined for displays in
Documentation/devicetree/bindings/display/panel/panel.txt .
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/devicetree/bindings/media/video-interfaces.txt

@@ -85,6 +85,10 @@ Optional properties
 
 - lens-focus: A phandle to the node of the focus lens controller.
 
+- rotation: The device, typically an image sensor, is not mounted upright,
+  but a number of degrees counter clockwise. Typical values are 0 and 180
+  (upside down).
+
 
 Optional endpoint properties
 ----------------------------