drivers/cpufreq: Update performance limits in EM

The cpufreq subsystem allows users to restrict the range of min/max
allowed frequencies. This can be done through:
  /sys/devices/system/cpu/cpufreq/policyX/scaling_[min|max]_freq

The Energy Aware Scheduler (EAS) relies on an Energy Model (EM) to
estimate the energy cost of placing a task on a CPU. To do a reliable
estimation, the EM must be aware of the min/max allowed frequencies.

Indeed, if the minimum allowed frequency is raised to NewMinFreq for
a policy, the cpufreq subsystem will account for this constraint when
selecting a frequency. However, the EAS currently assumes the
frequencies lower than NewMinFreq are also available. This can lead
to rigged energy estimation.

If a lower maximum frequency is set, cpufreq_update_pressure() allows
EAS to take into account this constraint. However, forbidden
frequencies should still be reflected in the EM.

Update the performance limits in the EM.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>