drm/i915: Dell Chromebook 11 has PWM backlight

Add quirk for Dell Chromebook 11 backlight.

Reported-and-tested-by: Owen Garland <garland.owen@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=93451


Acked-by: Damien Lespiau <damien.lespiau@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>