Platform: samsung_laptop: samsung backlight for R528/R728

patch works for me, but I need to add "acpi_backlight=vendor" to kernel
params

Signed-off-by: Smelov Andrey <xor29a@bk.ru>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Matthew Garrett <mjg@redhat.com>