Input: goodix - refer to touchscreen.txt in device tree bindings

Refer to touchscreen.txt for generic touch properties. This avoids
duplication and we're using the generic code to parse these in the
driver. While at that add touchscreen-size-{x,y} which are respected by
the driver as well.
Signed-off-by: NGuido Günther <agx@sigxcpu.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

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

@@ -19,11 +19,14 @@ Optional properties:
  - irq-gpios		: GPIO pin used for IRQ. The driver uses the
 			  interrupt gpio pin as output to reset the device.
  - reset-gpios		: GPIO pin used for reset
-
- - 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)
+ - touchscreen-inverted-x
+ - touchscreen-inverted-y
+ - touchscreen-size-x
+ - touchscreen-size-y
+ - touchscreen-swapped-x-y
+
+The touchscreen-* properties are documented in touchscreen.txt in this
+directory.
 
 Example: