HID: wacom: generic: Add support for battery status on pen and pad interfaces

Adds support for usages that may appear on the pen or pad interface which
report the state of the tablet battery.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>