Input: wacom - add support for EMR on Cintiq 24HD touch

Adds support for the EMR digitizer on the Cintiq 24HD touch. The
EMR digitizer should work identically to that found on the Cintiq
24HD. The touch digitizer is a separate USB device similar to how
we split apart some other devices.

Signed-off-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>