Add a CPU affinity set to the TCB if SMP is enable and use this CPU set as a...

Add a CPU affinity set to the TCB if SMP is enable and use this CPU set as a mask for determining which CPUs the thread may run on. Add an affinity field to the attrributes to permit controlling which CPUs a pthread may run on.  Implements pthread_att_setaffinity_np() and pthread_attr_getaffinity_np().