score: Introduce Thread_queue_Heads

Move the storage for the thread queue heads to the threads.  Each thread
provides a set of thread queue heads allocated from a dedicated memory
pool.  In case a thread blocks on a queue, then it lends its heads to
the queue.  In case the thread unblocks, then it takes a free set of
threads from the queue.  Since a thread can block on at most one queue
this works.  This mechanism is used in FreeBSD.  The motivation for this
change is to reduce the memory demands of the synchronization objects.
On a 32-bit uni-processor configuration the Thread_queue_Control size is
now 8 bytes, compared to 64 bytes in RTEMS 4.10 (other changes reduced
the size as well).

cpukit/sapi/include/confdefs.h

@@ -2969,6 +2969,8 @@ const rtems_libio_helper rtems_fs_init_helper =
 #define CONFIGURE_MEMORY_FOR_TASKS(_tasks, _number_FP_tasks) \
   ( \
     _Configure_Object_RAM(_tasks, sizeof(Configuration_Thread_control)) \
+      + _Configure_From_workspace(_Configure_Max_Objects(_tasks) \
+        * sizeof(Thread_queue_Heads)) \
       + _Configure_Max_Objects(_number_FP_tasks) \
         * _Configure_From_workspace(CONTEXT_FP_SIZE) \
   )