cpufreq: pxa3xx: move cpufreq driver to drivers/cpufreq

This patch moves cpufreq driver of ARM based pxa3xx platform to drivers/cpufreq.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>