ACPI: thinkpad-acpi: add sysfs led class support to thinkpad leds (v3.2)

Add a sysfs led class interface to the led subdriver.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Len Brown <len.brown@intel.com>