cpufreq: schedutil: map raw required frequency to driver frequency

cpufreq: schedutil: map raw required frequency to driver frequency

The slow-path frequency transition path is relatively expensive as it
requires waking up a thread to do work. Should support be added for
remote CPU cpufreq updates that is also expensive since it requires an
IPI. These activities should be avoided if they are not necessary.

To that end, calculate the actual driver-supported frequency required by
the new utilization value in schedutil by using the recently added
cpufreq_driver_resolve_freq API. If it is the same as the previously
requested driver frequency then there is no need to continue with the
update assuming the cpu frequency limits have not changed. This will
have additional benefits should the semantics of the rate limit be
changed to apply solely to frequency transitions rather than to
frequency calculations in schedutil.

The last raw required frequency is cached. This allows the driver
frequency lookup to be skipped in the event that the new raw required
frequency matches the last one, assuming a frequency update has not been
forced due to limits changing (indicated by a next_freq value of
UINT_MAX, see sugov_should_update_freq).

Signed-off-by: Steve Muckle <smuckle@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>