Introduce cpufreq micro benchmark

What is this benchmark for:
  - Identify worst case performance loss when doing dynamic frequency
    scaling using Linux kernel governors
  - Identify average reaction time of a governor to CPU load changes
  - (Stress) Testing whether a cpufreq low level driver or governor works
    as expected
  - Identify cpufreq related performance regressions between kernels
  - Possibly Real time priority testing? -> what happens if there are
    processes with a higher prio than the governor's kernel thread
  - ...

What this benchmark does *not* cover:
  - Power saving related regressions (In fact as better the performance
    throughput is, the worse the power savings will be, but the first should
    mostly count more...)
  - Real world (workloads)

Details how to use it can be found in the readme.
The benchmark got written by Christian Kornacker <ckornacker@suse.de>
and is published under the GNU General Public License.
(compare with copyright remarks inside the code).

cpufrequtils Makefile adjustments and some minor compile warning cleanups
came from:

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