serial: move delta_msr_wait into the tty_port

This is used by various drivers not just serial and can be extracted
as commonality

Signed-off-by: Alan Cox <alan@linux.intel.com>

drivers/char/tty_port.c

@@ -23,6 +23,7 @@ void tty_port_init(struct tty_port *port)
 	memset(port, 0, sizeof(*port));
 	init_waitqueue_head(&port->open_wait);
 	init_waitqueue_head(&port->close_wait);
+	init_waitqueue_head(&port->delta_msr_wait);
 	mutex_init(&port->mutex);
 	spin_lock_init(&port->lock);
 	port->close_delay = (50 * HZ) / 100;
@@ -124,6 +125,7 @@ void tty_port_hangup(struct tty_port *port)
 	port->tty = NULL;
 	spin_unlock_irqrestore(&port->lock, flags);
 	wake_up_interruptible(&port->open_wait);
+	wake_up_interruptible(&port->delta_msr_wait);
 	tty_port_shutdown(port);
 }
 EXPORT_SYMBOL(tty_port_hangup);