make current backlight value internally exported
make current backlight value internally exported

display system backends should be handling this in the event of changes, and being able to set it directly makes that easier

rvandegrift/e,rvandegrift/e,tasn/enlightenment,tasn/enlightenment,FlorentRevest/Enlightenment,tizenorg/platform.upstream.enlightenment,tizenorg/platform.upstream.enlightenment,tizenorg/platform.upstream.enlightenment,rvandegrift/e,tasn/enlightenment,FlorentRevest/Enlightenment,FlorentRevest/Enlightenment