HID: wacom: Allow dynamic battery creation/destruction

Tablets like the Intuos, Intuos Pro, and Bamboo have a connector for an
optional wireless module that can be connected on the fly. The presence
(or absence) of this module is indicated in a status report recieved
from the tablet. This patch adds a workqueue function that will create
or destroy a power_supply object at runtime to match the current state
of the WACOM_QUIRK_BATTERY flag.

Signed-off-by: Jason Gerecke <killertofu@gmail.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>