Input: wacom - add reporting of SW_MUTE_DEVICE events

New Intuos series models added a hardware switch to turn touch
data on/off. The state of the switch is reported periodically
from the tablet. To report the state the driver will emit SW_MUTE_DEVICE
events.

Reviewed_by: Chris Bagwell <chris@cnpbagwell.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>