rtems: Move scheduler directives to own header

Move all rtems_scheduler_* directives to the new header file
<rtems/rtems/scheduler.h>.  Add a Scheduler Manager API and
implementation group.

cpukit/include/rtems.h

@@ -73,6 +73,7 @@
 #include <rtems/rtems/part.h>
 #include <rtems/rtems/ratemon.h>
 #include <rtems/rtems/region.h>
+#include <rtems/rtems/scheduler.h>
 #include <rtems/rtems/sem.h>
 #include <rtems/rtems/signal.h>
 #include <rtems/rtems/status.h>

cpukit/include/rtems/rtems/tasksimpl.h

@@ -111,6 +111,14 @@ RTEMS_INLINE_ROUTINE rtems_task_priority _RTEMS_Priority_From_core(
 
 /**@}*/
 
+/**
+ * @defgroup RTEMSImplClassicScheduler Scheduler Manager
+ *
+ * @ingroup RTEMSImplClassic
+ *
+ * @brief This group contains the Scheduler Manager implementation.
+ */
+
 #if defined(RTEMS_MULTIPROCESSING)
 #include <rtems/rtems/taskmp.h>
 #endif