Add in required instruction serialization prior to releasing the

Add in required instruction serialization prior to releasing the
    MP lock for the last time.  The use of a locked instruction to
    cpu-private memory is 3x faster then CPUID and 3x faster then the
    use of a locked instruction to shared memory (the lock itself).

    Instruction serialization is required to ensure that any pending
    memory ops are properly flushed prior to the release of the lock,
    due to out-of-order instruction execution by the cpu.