drm/i915: add quirk to invert brightness on Packard Bell NCL20

commit 5559ecadad5a73b27f863e92f4b4f369501dce6f upstream.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44156
Reported-by: Alan Zimmerman <alan.zimm@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>