panic: Separate sysctl logic from CONFIG_SMP

In preparation for adding more sysctls directly in kernel/panic.c, split
CONFIG_SMP from the logic that adds sysctls.

Cc: Petr Mladek <pmladek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: tangmeng <tangmeng@uniontech.com>
Cc: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20221117234328.594699-1-keescook@chromium.org

kernel/panic.c

@@ -75,8 +75,9 @@ ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
 
 EXPORT_SYMBOL(panic_notifier_list);
 
-#if defined(CONFIG_SMP) && defined(CONFIG_SYSCTL)
+#ifdef CONFIG_SYSCTL
 static struct ctl_table kern_panic_table[] = {
+#ifdef CONFIG_SMP
 	{
 		.procname       = "oops_all_cpu_backtrace",
 		.data           = &sysctl_oops_all_cpu_backtrace,
@@ -86,6 +87,7 @@ static struct ctl_table kern_panic_table[] = {
 		.extra1         = SYSCTL_ZERO,
 		.extra2         = SYSCTL_ONE,
 	},
+#endif
 	{ }
 };