tty: create internal tty.h file

There are a number of functions and #defines in include/linux/tty.h that
do not belong there as they are private to the tty core code.

Create an initial drivers/tty/tty.h file and copy the odd "tty logging"
macros into it to seed the file with some initial things that we know
nothing outside of the tty core should be calling.

Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20210408125134.3016837-2-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index fdc4fa3..03f4141 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -19,6 +19,7 @@
 #include <linux/seq_file.h>
 #include <linux/uaccess.h>
 #include <linux/ratelimit.h>
+#include "tty.h"
 
 #undef LDISC_DEBUG_HANGUP