asus-laptop: add backlight support

Adds backlight support using backlight class. We now
change the brightness *and toggle the backlight !* via
/sys/class/backlight/asus-laptop/.

If the user switchs the backlight using the keyboard,
asus_hotk_notify looks for ATKD_LCD_OFF and ATKD_LCD_ON events,
and stores the right state into hotk->status and bd->props->power .

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 87e1db8..89bba27 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -75,6 +75,7 @@
         depends on ACPI
 	depends on EXPERIMENTAL && !ACPI_ASUS
 	depends on LEDS_CLASS
+	depends on BACKLIGHT_CLASS_DEVICE
         ---help---
 	  This is the new Linux driver for Asus laptops. It may also support some
 	  MEDION, JVC or VICTOR laptops. It makes all the extra buttons generate