ACPI: video: Add backlight=native DMI quirk for Apple iMac11,3

Linux defaults to picking the non-working ACPI video backlight interface
on the Apple iMac11,3 .

Add a DMI quirk to pick the working native radeon_bl0 interface instead.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>