I've always felt the backlight device conditional build has been all
backwards. Make it feel right.

Gently move things towards connector based stuff while at it.

There should be no functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>