arinc: add cpu-pool support to scheduler

arinc: add cpu-pool support to scheduler

1.  Remove the restriction that dom0 must be in the schedule, since dom-0 may
not belong to the scheduler's pool.
2.  Add a schedule entry for each of dom-0's vcpus as they are created.
3.  Add code to deal with empty schedules in the do_schedule function.
4.  Call the correct idle task for the pcpu on which the scheduling decision
is being made in do_schedule.
5.  Add code to prevent migration of a vcpu.
6.  Implement a proper cpu_pick function, which prefers the current processor.
7.  Add a scheduler lock to protect access to global variables from multiple
    PCPUs.

These changes do not implement arinc653 multicore.  Since the schedule only
supports 1 vcpu entry per slot, even if the vcpus of a domain are run on
multiple pcpus, the scheduler will essentially serialize their execution.

Signed-off-by: Nathan Studer <nate.studer@dornerworks.com>
Release-acked-by: George Dunlap <george.dunlap@eu.citrix.com>