pegasusq: Add flexrate capability

Ported cpufreq_ondemand_flexrate_request call compatibility to pegasusq and rewrote the main code in charge of handling the requests.

Added possibility to dismiss and cancel flexrate calls over a configurable maximum frequency.

Added hotplug sampling rate normalization during active flexrate requests; hotplug samples are delayed during accelerated governor sampling and are normalized to the usually active sampling rate.
pegasusq: Remove sysfs_duration from flexrate