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: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>