cpufreq: Fix broken uevents for cpufreq governor and cpu devices

cyanogens uevent commit when the governor changes was rendered
non-working since kitkat (or so) as the uevent filter function
caused events to be dropped. Now hook into cpufreq_core_init()
and cpufreq_add_dev_interface() to create our basic ksets for
cpufreq and cpu devices. Also, we don't need to set environmental
data, so clean it up a bit.

This commit requires a change in ueventd.rc that add rules for
several files of interest.

Commit: 9b2f1bf7dfbf1166fa82fc38a8cee611b10d1a2b