drm/i915: quirk backlight present on Macbook 4, 1

Unsurprisingly macbooks have backlights, just the VBT doesn't seem to
know it in this case.

Reported-and-tested-by: Daniel Nicoletti <dantti12@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88325


Fixes: c675949e ("drm/i915: do not setup backlight if not available according to VBT")
Cc: stable@vger.kernel.org # v3.15+
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446716999-1796-1-git-send-email-jani.nikula@intel.com