MFi386: revision 225936
MFi386: revision 225936

  Add some improvements in the idle table callbacks:
  - Replace instances of manual assembly instruction "hlt" call
    with halt() function calling.
  - In cpu_idle_mwait() avoid races in check to sched_runnable() using
    the same pattern used in cpu_idle_hlt() with the 'hlt' instruction.
  - Add comments explaining the logic behind the pattern used in
    cpu_idle_hlt() and other idle callbacks.

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