cpufreq: interactive: Simplify frequency calculations

Previously, complicated calculations led to oscillating cpu
frequencies that ruined user experience even on high-end
devices. Revert to the classic calculations based on a
percentage of current max frequency.  This way, we're using
freqs more evenly and much more predictable.
cpufreq: interactive: Consider changed min limit a frequency boost

A changed policy->min can safely be considered a frequency boost.
Process this change analogous to the cpufreq_interactive_boost()
routine.
cpufreq: interactive: Honor boosted state in several timer calculations