HID: logitech-hidpp: add support for battery status for the K750

The Solar Keyboard uses a different feature to report the battery level.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>