drm/i915: Ignore VBT backlight presence check on Acer C720 (4005U)

commit c675949e
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Wed Apr 9 11:31:37 2014 +0300

    drm/i915: do not setup backlight if not available according to VBT

prevents backlight setup on the Acer C720 (Core i3 4005U CPU), which has a
misconfigured VBT. Apply quirk to ignore the VBT backlight presence check
during backlight setup.

Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
Tested-by: Tyler Cleveland <siralucardt@openmailbox.org>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org (3.15+)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>