sched/cpufreq: uclamp: Add utilization clamping for RT tasks

Schedutil enforces a maximum frequency when RT tasks are RUNNABLE.
This mandatory policy can be made tunable from userspace to define a max
frequency which is still reasonable for the execution of a specific RT
workload while being also power/energy friendly.

Extend the usage of util_{min,max} to the RT scheduling class.

Add uclamp_default_perf, a special set of clamp values to be used
for tasks requiring maximum performance, i.e. by default all the non
clamped RT tasks.

Since utilization clamping applies now to both CFS and RT tasks,
schedutil clamps the combined utilization of these two classes.
The IOWait boost value is also subject to clamping for RT tasks.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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Changes in v6:
 Others:
 - wholesale s/group/bucket/
 - wholesale s/_{get,put}/_{inc,dec}/ to match refcount APIs