When the battery is neither charging or discharging and is not full,
"not-charging" is a useful status description for the case in general.
Currently this state is set as "unknown" by default, expect when this is
explicitly replaced with "not-charging" on a per device or per vendor
basis.

A lot of devices have this state without a BIOS specification available
explicitly describing it. e.g. some current Clevo barebones have a BIOS
setting to stop charging at a user defined battery level.
Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>