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.

tasks/mm0/src/vm_object.c

@@ -133,6 +133,9 @@ int vm_object_delete(struct vm_object *vmo)
 	/* Obtain and free via the base object */
 	if (vmo->flags & VM_OBJ_FILE) {
 		f = vm_object_to_file(vmo);
+		BUG_ON(!list_empty(&f->list));
+		if (f->priv_data)
+			kfree(f->priv_data);
 		kfree(f);
 	} else if (vmo->flags & VM_OBJ_SHADOW)
 		kfree(vmo);
@@ -141,3 +144,12 @@ int vm_object_delete(struct vm_object *vmo)
 	return 0;
 }
 
+int vm_file_delete(struct vm_file *f)
+{
+	/* Delete it from global file list */
+	list_del_init(&f->list);
+
+	/* Delete file via base object */
+	return vm_object_delete(&f->vm_obj);
+}
+