Add ondemandplus governor
-credit boype
ondemandplus: add and enable io_is_busy=2 option, adjust up_threshold and down_differential
cpufreq: ondemandplus: add missing else if

There is no need to check for a frequency decrease if an
increase has already been initialized. Must have forgot
the 'else' a long time ago and never noticed it. Anyway,
it's only a slight code improvement.