power: power_supply_core: Add API to enable and disable charging

To allow external drivers enable and disable charging add
a power supply framework property POWER_SUPPLY_PROP_CHARGING_ENABLED
which reflects the status of charging being enabled or disabled.

Change-Id: I199a08797b8f2f00edee05e83735c4835400aa60
Signed-off-by: David Keitel <dkeitel@codeaurora.org>
diff --git a/drivers/power/power_supply_sysfs.c b/drivers/power/power_supply_sysfs.c
index 4368e7d..7eb285b 100644
--- a/drivers/power/power_supply_sysfs.c
+++ b/drivers/power/power_supply_sysfs.c
@@ -138,6 +138,7 @@
 	POWER_SUPPLY_ATTR(health),
 	POWER_SUPPLY_ATTR(present),
 	POWER_SUPPLY_ATTR(online),
+	POWER_SUPPLY_ATTR(charging_enabled),
 	POWER_SUPPLY_ATTR(technology),
 	POWER_SUPPLY_ATTR(cycle_count),
 	POWER_SUPPLY_ATTR(voltage_max),