cpufreq: ondemand: Clean up

Remove useless code and correct the previously wrong merge

Signed-off-by: Kostas K <mpokwsths@gmail.com>
cpufreq: ondemand: Use hotplug thread infrastructure

The dbs_sync threads caused considerable load, even when ondemand
wasn't even active. Use the hotplug thread infrastructure to park
the threads.
defconfig: Update

Signed-off-by: Kostas K <mpokwsths@gmail.com>