console: Introduce ->exit() callback

Some consoles might require special operations on unregistering.
For instance, serial console, when registered in the kernel,
keeps power on for entire time, until it gets unregistered.
Example of use:

	->setup(console):
		pm_runtime_get(...);

	->exit(console):
		pm_runtime_put(...);

For such cases to have a balance we would provide ->exit() callback.

Link: http://lkml.kernel.org/r/20200203133130.11591-7-andriy.shevchenko@linux.intel.com
To: linux-kernel@vger.kernel.org
To: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

include/linux/console.h

@@ -149,6 +149,7 @@ struct console {
 	struct tty_driver *(*device)(struct console *, int *);
 	void	(*unblank)(void);
 	int	(*setup)(struct console *, char *);
+	int	(*exit)(struct console *);
 	int	(*match)(struct console *, char *name, int idx, char *options);
 	short	flags;
 	short	index;

kernel/printk/printk.c

@@ -2853,6 +2853,9 @@ int unregister_console(struct console *console)
 	console_unlock();
 	console_sysfs_notify();
 
+	if (console->exit)
+		res = console->exit(console);
+
 	return res;
 
 out_disable_unlock: