sys/kern: Add lockmgr support

- See `man lockmgr`

- Implement the lock_object and move the RTEMS mutex to that object

- Add debug support to track the locks with gdb

Update #4475

rtemsbsd/include/machine/rtems-bsd-thread.h

@@ -45,6 +45,7 @@
 #include <sys/proc.h>
 
 #include <rtems.h>
+#include <rtems/score/thread.h>
 
 extern sbintime_t rtems_bsd_sbt_per_watchdog_tick;