hvc_console: Add a hangup notifier for backends

I have added a hangup notifier that can be used by hvc console
backends to handle a tty hangup. The default irq hangup notifier
calls the notifier_del_irq() for compatibility.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index d0f4eb6..3fb0d2c 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -198,6 +198,7 @@
 	virtio_cons.put_chars = put_chars;
 	virtio_cons.notifier_add = notifier_add_vio;
 	virtio_cons.notifier_del = notifier_del_vio;
+	virtio_cons.notifier_hangup = notifier_del_vio;
 
 	/* The first argument of hvc_alloc() is the virtual console number, so
 	 * we use zero.  The second argument is the parameter for the