HID: expose wacom pen tablet battery through power_supply class

This patch exposes wacom pen tablet battery capacity and ac state thru
power_supply class is sysfs.

Signed-off-by: Przemo Firszt <przemo@firszt.eu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index 71d4c07..8e1b505 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -357,6 +357,14 @@
 	---help---
 	Support for Wacom Graphire Bluetooth tablet.
 
+config HID_WACOM_POWER_SUPPLY
+	bool "Wacom Bluetooth devices power supply status support"
+	depends on HID_WACOM
+	select POWER_SUPPLY
+	---help---
+	  Say Y here if you want to enable power supply status monitoring for
+	  Wacom Bluetooth devices.
+
 config HID_ZEROPLUS
 	tristate "Zeroplus based game controller support" if EMBEDDED
 	depends on USB_HID