HID: logitech-hidpp: add battery support for HID++ 2.0 devices
If the 0x1000 Unified Battery Level Status feature exists, expose the battery
level.
The main drawback is that while a device is plugged in its battery level is 0.
To avoid exposing that as 0% charge we make up a number based on the charging
status.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>