sysctl: move umh sysctl registration to its own file

Move the umh sysctl registration to its own file, the array is
already there. We do this to remove the clutter out of kernel/sysctl.c
to avoid merge conflicts.

This also lets the sysctls not be built at all now when CONFIG_SYSCTL
is not enabled.

This has a small penalty of 23 bytes but soon we'll be removing
all the empty entries on sysctl arrays so just do this cleanup
now:

./scripts/bloat-o-meter vmlinux.base vmlinux.1
add/remove: 2/0 grow/shrink: 0/1 up/down: 49/-26 (23)
Function old new delta
init_umh_sysctls - 33 +33
__pfx_init_umh_sysctls - 16 +16
sysctl_init_bases 111 85 -26
Total: Before=21256914, After=21256937, chg +0.00%

Acked-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Luis Chamberlain <[e-mail]>

include/linux/umh.h

···
 extern int
 call_usermodehelper_exec(struct subprocess_info *info, int wait);
 
-extern struct ctl_table usermodehelper_table[];
-
 enum umh_disable_depth {
 	UMH_ENABLED = 0,
 	UMH_FREEZING,

kernel/sysctl.c

···
 int __init sysctl_init_bases(void)
 {
 	register_sysctl_init("kernel", kern_table);
-	register_sysctl_init("kernel/usermodehelper", usermodehelper_table);
 #ifdef CONFIG_KEYS
 	register_sysctl_init("kernel/keys", key_sysctls);
 #endif

kernel/umh.c

···
 	return 0;
 }
 
-struct ctl_table usermodehelper_table[] = {
+#if defined(CONFIG_SYSCTL)
+static struct ctl_table usermodehelper_table[] = {
 	{
 		.procname	= "bset",
 		.data		= &usermodehelper_bset,
···
 	},
 	{ }
 };
+
+static int __init init_umh_sysctls(void)
+{
+	register_sysctl_init("kernel/usermodehelper", usermodehelper_table);
+	return 0;
+}
+early_initcall(init_umh_sysctls);
+#endif /* CONFIG_SYSCTL */