thinkpad_acpi: Add support for battery thresholds

1) Charge start threshold
/sys/class/power_supply/BATN/charge_start_threshold

Valid values are [0, 99]. A value of 0 turns off the
start threshold wear control.

2) Charge stop threshold
/sys/class/power_supply/BATN/charge_stop_threshold

Valid values are [1, 100]. A value of 100 turns off
the stop threshold wear control. This must be
configured first.

Signed-off-by: Ognjen Galic <smclt30p@gmail.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/platform/x86/Kconfig

@@ -425,6 +425,7 @@ config SURFACE3_WMI
 config THINKPAD_ACPI
 	tristate "ThinkPad ACPI Laptop Extras"
 	depends on ACPI
+	depends on ACPI_BATTERY
 	depends on INPUT
 	depends on RFKILL || RFKILL = n
 	depends on ACPI_VIDEO || ACPI_VIDEO = n