ACPI / video: Favor native backlight interface for ThinkPad Helix

Like many other Windows 8 laptops the ThinkPad Helix's backlight has a
broken ACPI interface and can only be properly adjusted by using the
video card's native backlight control. This adds the ThinkPad Helix to
the list of laptops affected with this issue so that
video.use_native_backlight is enabled by default.

Signed-off-by: Stephen Chandler Paul <thatslyude@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>