drm/i915: Expose adaptive backlight properties on LVDS connectors.

drm/i915: Expose adaptive backlight properties on LVDS connectors.

So far we only exposed it on eDP connectors. Let's also expose it on LVDS.

BUG=none
TEST=by hand, ran xrandr --verbose and checked the adaptive backlight
TEST=property is here

Change-Id: I70d836ff437ace10acf59c780aa5f06428ecef58
Reviewed-on: https://gerrit.chromium.org/gerrit/33098
Tested-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Commit-Ready: Stéphane Marchesin <marcheu@chromium.org>