cpufreq/zzmoove: added tuneables for fastdown

fastdown dynamically applies a (presumably) higher up_threshold after a
frequency threshold has been reached. the goal is to encourage less time
spent on the highest frequencies.

- added fastdown_freq (0 = disabled)
	fastdown will be enabled once this frequency has been met or exceeded.
- added fastdown_up_threshold
	once the above frequency threshold has been met, this will become
	the new up_threshold until we fall below the fastdown_freq again.

based on commits to pegasusq in perseus by andreilux.