kernel: Simplified idle for SMP auxiliary CPUs

A pure timer-based idle won't work well in SMP.  Without an IPI to
wake up idle CPUs out of the scheduler they will sleep far too long
and the main CPU will do all the scheduling of wake-up-and-sleep
processes.  Instead just have the auxilary CPUs do a traditional
busy-wait scheduler in their idle loop.

We will need to revisit an architecture that allows both
wait-for-timer-interrupt idle and SMP.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>