Intuos4 WL is separately reporting power supply and battery
charging status - now hid-wacom is using that information.
Previously hid-wacom was wrongly treating "battery charging" bit
as "power supply connected". Now it should report battery charging,
battery discharging, battery full and power supply status.

Intuos4 WL sends reports when is in use (obvious) and when unplugging
power supply. If means that if the device is being charged, but it's not
being used it will never report "battery full". The same problem happens
after the device has been connected, but it's not in use - the
battery/ac status will be incorrect. Currently there is no mechanism to
ask the device to send a report containing battery/ac status.
Signed-off-by: Przemo Firszt <przemo@firszt.eu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>