power_supply: Add "unknown" in power supply type

For the default value of power supply type, "unknown" is added.
With default prop value, supply type property can be displayed
as default - "Unknown".

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>
diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index 204c18d..9c83e04 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -123,7 +123,8 @@
 };
 
 enum power_supply_type {
-	POWER_SUPPLY_TYPE_BATTERY = 0,
+	POWER_SUPPLY_TYPE_UNKNOWN = 0,
+	POWER_SUPPLY_TYPE_BATTERY,
 	POWER_SUPPLY_TYPE_UPS,
 	POWER_SUPPLY_TYPE_MAINS,
 	POWER_SUPPLY_TYPE_USB,		/* Standard Downstream Port */