printk: add dummy printk_force_console_enter/exit helpers

The newly added interface is broken when PRINTK is disabled:

drivers/tty/sysrq.c: In function '__handle_sysrq':
drivers/tty/sysrq.c:601:9: error: implicit declaration of function 'printk_force_console_enter' [-Wimplicit-function-declaration]
  601 |         printk_force_console_enter();
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/tty/sysrq.c:611:25: error: implicit declaration of function 'printk_force_console_exit' [-Wimplicit-function-declaration]
  611 |                         printk_force_console_exit();
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~

Add empty stub functions for both.

Fixes: ed76c07 ("printk: Introduce FORCE_CON flag")
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Marcos Paulo de Souza <[email protected]>
Tested-by: Marcos Paulo de Souza <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

include/linux/printk.h

@@ -232,6 +232,14 @@ static inline void printk_deferred_exit(void)
 {
 }
 
+static inline void printk_force_console_enter(void)
+{
+}
+
+static inline void printk_force_console_exit(void)
+{
+}
+
 static inline int printk_ratelimit(void)
 {
 	return 0;