tty: Introduce a tty_port generic block_til_ready

Start sucking more commonality out of the drivers into a single piece of
core code.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/synclink.c

@@ -3401,6 +3401,7 @@ static int block_til_ready(struct tty_struct *tty, struct file * filp,
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&port->open_wait, &wait);
 	
+	/* FIXME: Racy on hangup during close wait */
 	if (extra_count)
 		port->count++;
 	port->blocked_open--;