From: john stultz <johnstul@us.ibm.com>

This is a rework of John's recent change which resolved a circular include
dependency: a function in mach_apic.h requires hard_smp_processor_id() and
hard_smp_processor_id() requires macros from mach_apic.h

So this patch (against bk-current) reverts the previous, and fixes the same
circular dependency in a much cleaner way, by moving a piece of the circular
chain into its own .h file, rather then removing hard_smp_processor_id() and
accessing the apic by hand.