Input: wacom - specify Cinitq supported tools

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: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>