[cpu-daemon] userspace cpufreq dynamic changes are available

[external apis]
- read_scaling_governor : read the governor in enum
    (ADAPTIVE, INTERACTIVE, CONSERVATIVE, USERSPACE, POWERSAVE, ONDEMAND, PERFORMANCE)
- set_scaling_governor : change the governor, careful of enum type
- set_cpufreq_to_max : change the governor to userspace if it is not,
    set the maximum frequency
- set_cpufreq_to_min : change the governor to userspace if it is not,
    set the minimum frequency
- set_cpufreq_to_value : change the governor to userspace if it is not,
    change to the given frequency
- read_scaling_cur_freq : read the current frequency
- get_next_freq : get the next higher step of the current frequency
- set_cpufreq_to_next_step : set to the next higher step of the current frequency
- get_prev_freq : get the previous lower step of the current frequency
- set_cpufreq_to_prev_step : set to the previous lower step of the current frequency