cpufreq: interactive: Honor changed minimum frequency

This saves a few cycles in the timer routine.
cpufreq: interactive: Use parts of native boost routine

Not all governors are created equal. Set boostpulse_endtime
and floor_freq to smoothen the timer routine.
cpufreq: interactive: Use frequency dependent per cpu timings

This allows in-depth testing of the timer routine.
cpufreq: interactive: Honor boosted state when entering idle

The old logic didn't take the boosted state in account. Just
leave the comment intact because our temporary min is not
the regular policy->min it refers to.