drm/i915: Pass connector state to intel_panel_set_backlight_acpi

Passing the state is also needed to convert the backlight functions
to use the correct state instead of looking it up.

This is done as a separate commit to allow easier bisecting.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100022


Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170612102115.23665-3-maarten.lankhorst@linux.intel.com


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>