cpufreq: Add cpu utilization statistics to aid decisions made by userspace.

Understanding system load as seen by cpufreq can help userspace
algorithms make better decisions to improve system responsiveness.
One such example would be the MP decision algorithm which mines
various system info to make decisions on hotplugging in/out
the additional cores.

Change-Id: I277db7e1a7803a3822b61e7befa25131487cfe17