Multiple updates on sleeping, vma dropping and thread suspend.

- Updated sleeping paths such that a task is atomically put into
  a runqueue and made RUNNABLE, or removed from a runqueue and made SLEEPING.
- Modified vma dropping sources to handle both copy_on_write() and exit() cases
  in a common function.
- Added the first infrastructure to have a pager to suspend a task and wait for
  suspend completion from the scheduler.

include/l4/generic/scheduler.h

@@ -37,6 +37,7 @@ static inline struct ktcb *current_task(void)
 #define need_resched		(current->ts_need_resched)
 
 void sched_init_task(struct ktcb *task, int priority);
+void sched_prepare_sleep(void);
 void sched_resume_sync(struct ktcb *task);
 void sched_resume_async(struct ktcb *task);
 void scheduler_start(void);

include/l4/generic/tcb.h

@@ -25,8 +25,7 @@
 #define TASK_SUSPENDING			(1 << 1)
 #define TASK_RESUMING			(1 << 2)
 
-
-/* Scheduler states */
+/* Task states */
 enum task_state {
 	TASK_INACTIVE	= 0,
 	TASK_SLEEPING	= 1,
@@ -52,6 +51,7 @@ struct ktcb {
 
 	/* Runqueue related */
 	struct list_head rq_list;
+	struct runqueue *rq;
 
 	/* Thread information */
 	l4id_t tid;		/* Global thread id */
@@ -91,6 +91,9 @@ struct ktcb {
 	struct waitqueue_head wqh_send;
 	l4id_t expected_sender;
 
+	/* Waitqueue for pagers to wait for task states */
+	struct waitqueue_head wqh_pager;
+
 	/* Tells where we are when we sleep */
 	struct spinlock waitlock;
 	struct waitqueue_head *waiting_on;