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().

include/pthread.h

@@ -178,6 +178,10 @@ struct pthread_attr_s
   uint8_t max_repl;            /* Maximum pending replenishments */
 #endif
 
+#ifdef CONFIG_SMP
+  cpu_set_t affinity;          /* Set of permitted CPUs for the thread */
+#endif
+
   size_t stacksize;            /* Size of the stack allocated for the pthread */
 
 #ifdef CONFIG_SCHED_SPORADIC