[VBFS] modify frequency change rule by CPU load

frequency change by CPU load was currently step up or down,
this will be changed to scale up or down in the range of min and max
according to the current CPU load

ondemand and vbfs logs of "/data/cpulog/cpulog2.txt" will be activated by
writing # seconds to "/sys/devices/system/cpu/cpu0/cpufreq/status_monitor"

use "adb pull /data/cpulog/cpulog2.txt" to pull out the log