tty: create internal tty.h file

[ Upstream commit 98602c010ceba82f2c2384122dbd07bc965fd367 ]

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>
Stable-dep-of: 094fb49a2d0d ("tty: Prevent writing chars during tcsetattr TCSADRAIN/FLUSH")
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/tty/tty_port.c

@@ -18,6 +18,7 @@
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/serdev.h>
+#include "tty.h"
 
 static int tty_port_default_receive_buf(struct tty_port *port,
 					const unsigned char *p,