The HP Pavilion dv6 has a non-working acpi_video0 backlight interface
and an intel_backlight interface which works fine. Add a force_native
quirk for it so that the non-working acpi_video0 interface does not get
registered.

Note that there are quite a few HP Pavilion dv6 variants, some
woth ATI and some with NVIDIA hybrid gfx, both seem to need this
quirk to have working backlight control. There are also some versions
with only Intel integrated gfx, these may not need this quirk, but it
should not hurt there.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1204476
Link: https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1416940
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>