vt: Initialize conswitchp to dummy_con if unset

If the arch setup code hasn't initialized conswitchp yet, set it to
dummy_con in con_init. This will allow us to drop the dummy_con
initialization that's done in almost every architecture.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20191218214506.49252-3-nivedita@alum.mit.eduSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -3326,7 +3326,8 @@ static int __init con_init(void)
 
 	console_lock();
 
-	if (conswitchp)
+	if (!conswitchp)
+		conswitchp = &dummy_con;
 	display_desc = conswitchp->con_startup();
 	if (!display_desc) {
 		fg_console = 0;