media: dt: bindings: Add strobe property for CCP2

Document the CSI1/CCP2 property strobe. It signifies the clock or
strobe mode.
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NIvaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: NPavel Machek <pavel@ucw.cz>
Reviewed-by: NSebastian Reichel <sre@kernel.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

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

@@ -117,7 +117,8 @@ Optional endpoint properties
   should be the combined length of data-lanes and clock-lanes properties.
   If the lane-polarities property is omitted, the value must be interpreted
   as 0 (normal). This property is valid for serial busses only.
-
+- strobe: Whether the clock signal is used as clock (0) or strobe (1). Used
+  with CCP2, for instance.
 
 Example
 -------