cpufreq: interactive: Add a sampling_down_factor for max frequencies

Change min_sample_time to sampling_down_factor ms when running at max
frequency. This would keep the frequency up at max for at least that much
time before allowing it to step down. This is an important performance
enhancement for CPU intensive workloads like benchmarks where there is
consistently high load on CPU to keep it up at max frequency.

Change-Id: Ia7e35b0625bedf20e7ef3a1f52e5828ffbfed93e
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>