tty: disable unbind for old 74xx based serial/mpsc console port

We recently got rid of some modular code in this driver and also
got rid of the unused ".remove" function at the same time.  Thierry
noted that it was however possible to force the remove through the
bind/unbind interface.

Since this is a console device used on 2005 vintage 74xx based
powerpc embedded targets, and is essentially always used in
conjunction with SERIAL_MPSC_CONSOLE=y -- there is no sane reason
anyone would ever want to unbind the builtin driver and lose the
console.  So we just explicitly block bind/unbind operations and
prevent root from shooting themselves in the foot.

Cc: Greg Kroah-Hartman <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Paul Gortmaker <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Paul Gortmaker

drivers/tty/serial/mpsc.c

@@ -2109,7 +2109,8 @@ static int mpsc_drv_probe(struct platform_device *dev)
 static struct platform_driver mpsc_driver = {
 	.probe	= mpsc_drv_probe,
 	.driver	= {
-		.name	= MPSC_CTLR_NAME,
+		.name			= MPSC_CTLR_NAME,
+		.suppress_bind_attrs	= true,
 	},
 };