cpufreq: unicore2: move cpufreq driver to drivers/cpufreq

This patch moves cpufreq driver of UNICORE-2 architecture to drivers/cpufreq.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>