cpufreq: Re-arrange declarations in cpufreq.h

They are pretty much mixed up.  Although generic headers are present,
definitions/declarations are present outside of them too ...

This patch just moves stuff up and down to make it look better and
consistent.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>