tty: replace BKL with a new tty_lock

As a preparation for replacing the big kernel lock
in the TTY layer, wrap all the callers in new
macros tty_lock, tty_lock_nested and tty_unlock.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/briq_panel.c b/drivers/char/briq_panel.c
index 555cd93..d5fa113 100644
--- a/drivers/char/briq_panel.c
+++ b/drivers/char/briq_panel.c
@@ -67,15 +67,15 @@
 
 static int briq_panel_open(struct inode *ino, struct file *filep)
 {
-	lock_kernel();
+	tty_lock();
 	/* enforce single access, vfd_is_open is protected by BKL */
 	if (vfd_is_open) {
-		unlock_kernel();
+		tty_unlock();
 		return -EBUSY;
 	}
 	vfd_is_open = 1;
 
-	unlock_kernel();
+	tty_unlock();
 	return 0;
 }