The old /proc/sys/cpu/ - based interface is nothing else than a
cpufreq governor which decides what frequency to use within a policy
based on userspace input. So, convert this interface (and add a
corresponding sysfs file, /sys/devices/sys/cpu0/scaling_setspeed) to
become a cpufreq governor, and move it out to an extra module (which
partly explains the size of this patch).