ACPI video: dmi check for broken _BQC on Acer Aspire 5720

On Acer Aspire 5720, _BQC always returns a value 9 smaller than
the actual brightness level.  Add dmi quirk for this laptop.

http://bugzilla.kernel.org/show_bug.cgi?id=13121

Tested-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>