tty: BKL pushdown

- Push the BKL down into the line disciplines
- Switch the tty layer to unlocked_ioctl
- Introduce a new ctrl_lock spin lock for the control bits
- Eliminate much of the lock_kernel use in n_tty
- Prepare to (but don't yet) call the drivers with the lock dropped
  on the paths that historically held the lock

BKL now primarily protects open/close/ldisc change in the tty layer

[jirislaby@gmail.com: a couple of fixes]
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/compat_ioctl.c

@@ -1046,7 +1046,7 @@ static int vt_check(struct file *file)
 	struct inode *inode = file->f_path.dentry->d_inode;
 	struct vc_data *vc;
 	
-	if (file->f_op->ioctl != tty_ioctl)
+	if (file->f_op->unlocked_ioctl != tty_ioctl)
 		return -EINVAL;
 	                
 	tty = (struct tty_struct *)file->private_data;