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>