drm: i915: Port to new backlight interface selection API

This results in a nice cleanup, as we can replace the complicated logic
from should_ignore_backlight_request() with a simple check for the type
being native.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>