ACPI / video: disable native backlight for ThinkPad X201s

The ThinkPad X201s has a working ACPI video backlight interface and is
shipped before Win8; then there is BIOS update that starts to query
_OSI("Windows 2012") and that would make our video module stop creating
backlight interface and caused problem for the user. Add it to the DMI
table to disable native backlight to fix this problem.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=81691
Link: https://bugzilla.kernel.org/show_bug.cgi?id=51231
Cc: 3.16+ <stable@vger.kernel.org> # 3.16+
Reported-and-tested-by: Yves-Alexis Perez <corsac@debian.org>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>