Input: touchscreen DT binding - add touchscreen-swapped-x-y property

On devices with a native portrait screen a landscape touchscreen /
digitizer may be used, this happens e.g. on ebook readers. In this case the
X and Y axis of the touchscreen are swapped compared to the screen.

Add a touchscreen-swapped-x-y property which drivers can use to see if they
need to swap the axis to make the touchscreen coordinates match the screen
coordinates.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt

@@ -16,6 +16,8 @@ Optional properties for Touchscreens:
 				  controller)
  - touchscreen-inverted-x	: X axis is inverted (boolean)
  - touchscreen-inverted-y	: Y axis is inverted (boolean)
+ - touchscreen-swapped-x-y	: X and Y axis are swapped (boolean)
+				  Swapping is done after inverting the axis
 
 Deprecated properties for Touchscreens:
  - x-size			: deprecated name for touchscreen-size-x