Cintiq, being a display tablet, doesn't have mouse and associated BTN_s.
Make sure we do not specify them when registering Cintiq's input device
so that userland can retrieve the exact tool set the device supports.
Signed-off-by: NPing Cheng <pingc@wacom.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>