power: supply: wilco_ec: Add long life charging mode

This is a long life mode set in the factory for extended warranty
battery, the power charging rate is customized so that battery at
work last longer.

Presently switching to a different battery charging mode is through
EC PID 0x0710 to configure the battery firmware, this operation will
be blocked by EC with failure code 0x01 when PLL mode is already
in use.

Signed-off-by: Crag Wang <crag.wang@dell.com>
Reviewed-by: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/ABI/testing/sysfs-class-power-wilco

@@ -14,6 +14,10 @@ Description:
 			Charging begins when level drops below
 			charge_control_start_threshold, and ceases when
 			level is above charge_control_end_threshold.
+		Long Life: Customized charge rate for last longer battery life.
+			On Wilco device this mode is pre-configured in the factory
+			through EC's private PID. Swiching to a different mode will
+			be denied by Wilco EC when Long Life mode is enabled.
 
 What:		/sys/class/power_supply/wilco-charger/charge_control_start_threshold
 Date:		April 2019