cpufreq: interactive: Allow frequency drop during max_freq_hysteresis

max_freq_hysteresis keeps CPU at policy->max even after load goes
away. This is necessary for some workloads where heavy task start and
stop often. However, in case heavy task indeed stops, it's not very
power friendly to stay at policy->max for extended period.

Instead of keeping CPU at policy->max, drop frequency optimistically.
If a heavy load starts back up again and hit go_hispeed_load within
max_freq_hysteresis period, directly ramp back up to policy->max.

Change-Id: I5edf6d765a3599a5b26e13e584bd237e932593f0
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>