drm/i915: add quirk to invert brightness on eMachines G725

commit 1ffff60320879830e469e26062c18f75236822ba upstream.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=59628
Reported-by: Roland Gruber <post@rolandgruber.de>
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>
[wml: Backported to 3.4: Adjust context]
Signed-off-by: Weng Meiling <wengmeiling.weng@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>