some variables definition are gathered to fork_tree_node from process.

- remove both-defined: pid, pgid, status
- move to fork_tree_node: tid
- make dummy fork_tree_node for idle_process.

kernel/include/cls.h

@@ -41,6 +41,7 @@ struct cpu_local_var {
 	ihk_spinlock_t free_list_lock;
 
 	struct process idle;
+	struct fork_tree_node idle_ftn;
 	struct process_vm idle_vm;
 
 	ihk_spinlock_t runq_lock;