cpufreq-bench: Add plot helper scripts

- cpufreq-bench_plot.sh
   Plots nice pictures based on cpufreq-bench logs

 - cpufreq-bench_script.sh
   Modifies ondemand variables, runs cpufreq-bench and creates plots

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>