x86 platform drivers: make Dell laptop driver select needed LED support

Otherwise we get compile errors like this:

  ERROR: "led_classdev_unregister" [drivers/platform/x86/dell-laptop.ko] undefined!
  ERROR: "led_classdev_register" [drivers/platform/x86/dell-laptop.ko] undefined!
  make[1]: *** [__modpost] Error 1
  make: *** [modules] Error 2

when the dell-laptop support is enabled without the necessary LED
support being enabled.
Reported-by: Alessandro Suardi <alessandro.suardi@gmail.com>
Acked-by: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/platform/x86/Kconfig

@@ -85,6 +85,8 @@ config DELL_LAPTOP
 	depends on RFKILL || RFKILL = n
 	depends on POWER_SUPPLY
 	depends on SERIO_I8042
+	select LEDS_CLASS
+	select NEW_LEDS
 	default n
 	---help---
 	This driver adds support for rfkill and backlight control to Dell