Mutex implementation almost working.

- Fixed a wrong instruction in mutex.S user library
- Added support for blocking lock/unlock
- Divided waiting into wait_on_prepare and wait_on_prepared_wait
  so that mutex_control lock is released after getting in the waitqueue.
- Declaring waitqueue on the stack should be done outside wait_on_prepare

Issues:
- Tests can be simplified for atomic data access instead of producer/consumer.
- kmalloc variable sized memory caches are not freed properly. Currently only the
  last slot can be freed, occupied correctly. it should be done in any slot, i.e.
  1, 2, 3, 4 instead of just 5.
- Need to add a mutex to kmalloc.

include/l4/lib/wait.h

@@ -77,6 +77,7 @@ int wake_up_task(struct ktcb *task, unsigned int flags);
 void wake_up_all(struct waitqueue_head *wqh, unsigned int flags);
 
 int wait_on(struct waitqueue_head *wqh);
-
+int wait_on_prepare(struct waitqueue_head *wqh, struct waitqueue *wq);
+int wait_on_prepared_wait(void);
 #endif /* __LIB_WAIT_H__ */