display: Ensure we list available scaling values keeping the same distribution
A display might support lots of scaling values, but gnome-control-center does not show more than 5 possibilities, and these values are just limited by the collected number. So, when multiple scaling values are advertised, we just show the first listed elements.
While it's correct to limit the values to show, we should ensure that we keep the distribution and that at least the minimum and maximum advertised scaling levels are shown.
So, in case we have a number of appliable scaling that is more or equal than MAX_N_SCALES, we need to make sure that at least we list the minimum, maximum and current scaling, and then distribute the other available scaling values keeping a linear progression.