Progress on capabilities

Capabilities will be shared among collection of threads. A pager
will have a right to share its own capabilities with its space,
its thread group and its container.

Currently sharing is possible with only all of the caps. Next,
it will be support for cap splitting, granting, and partial sharing
and granting.

include/l4/lib/list.h

@@ -73,6 +73,18 @@ static inline void list_remove_init(struct link *link)
 	link->prev = link;
 }
 
+/* Cuts the whole list from head and returns it */
+static inline struct link *list_detach(struct link *head)
+{
+	struct link *next = head->next;
+
+	/* Detach head from rest of the list */
+	list_remove_init(head);
+
+	/* Return detached list */
+	return next;
+}
+
 static inline int list_empty(struct link *list)
 {
 	return list->prev == list && list->next == list;