scheduler: low_latency: Try to keep all cores busy
scheduler: Cache quantum length
Revert "scheduler: SCHEDULER_EXIT_FUNCTION() is not needed"

This reverts commit 667617ad043a4587d8d366d5192d9ad291cfa37a.

Scheduler profiler uses CPU local data to store function information, hence
arch_thread_context_switch() usually is not a problem. However, when
we switch to a new thread we end up scheduler_new_thread_entry() instead
of scheduler_reschedule() what may corrupt data collected by the profiler.