Input: wacom - enhance Wireless Receiver battery reporting

- Reports the current status of the battery (discharging, charging, full).
- Also notify the upower daemon when there is a change in the battery
  value.
- keep the battery value as a percentage, not the raw value
- add WACOM_QUIRK_BATTERY to easily add a battery to a device (required
  for Bluetooth devices)

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Przemo Firszt <przemo@firszt.eu>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
diff --git a/drivers/hid/wacom.h b/drivers/hid/wacom.h
index a678f82..98cb93f 100644
--- a/drivers/hid/wacom.h
+++ b/drivers/hid/wacom.h
@@ -128,6 +128,13 @@
 	schedule_work(&wacom->work);
 }
 
+static inline void wacom_notify_battery(struct wacom_wac *wacom_wac)
+{
+	struct wacom *wacom = container_of(wacom_wac, struct wacom, wacom_wac);
+
+	power_supply_changed(&wacom->battery);
+}
+
 extern const struct hid_device_id wacom_ids[];
 
 void wacom_wac_irq(struct wacom_wac *wacom_wac, size_t len);