can be thought of as a percentage.
But some buggy _BQC/_BCL/_BCM methods use the index values instead.
http://bugzilla.kernel.org/show_bug.cgi?id=12302
http://bugzilla.kernel.org/show_bug.cgi?id=12249
http://bugzilla.kernel.org/show_bug.cgi?id=12037

Add the functionality to support such kind of BIOSes in ACPI video driver.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Matthew Garrett <mjg59@srcf.ucam.org>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>