luci-app-statistics: cpufreq: enhance additional data

* Use the new data series sorting and coloring options to
  display the frequencies in order and with matching coloring in
  different cores.

* Fix the y-axis text and legend in the frequency usage graph

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>
(cherry picked from commit 05cad423ce)

applications/luci-app-statistics/luasrc/statistics/rrdtool/definitions/cpufreq.lua

@@ -42,12 +42,13 @@ function rrdargs( graph, plugin, plugin_instance, dtype )
 	local percentage = {
 		title = "%H: Frequency distribution - core %pi",
 		alt_autoscale = true,
-		vlabel = "Frequency (Hz)",
+		vlabel = "Percent",
 		number_format = "%5.2lf%%",
+		ordercolor = true,
 		data = {
 			types = { "percent" },
 			options = {
-				percent = { title = "Frequency %di" },
+				percent = { title = "%di Hz", negweight = true },
 			}
 		}
 	}