Platform: samsung_laptop: add support for X520 machines.

my samsung laptop would be very happy if you add
these lines to the file drivers/platform/x86/samsung-laptop.c

Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Matthew Garrett <mjg@redhat.com>