LSM: Add /sys/kernel/security/lsm

I am still tired of having to find indirect ways to determine
what security modules are active on a system. I have added
/sys/kernel/security/lsm, which contains a comma separated
list of the active security modules. No more groping around
in /proc/filesystems or other clever hacks.

Unchanged from previous versions except for being updated
to the latest security next branch.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.l.morris@oracle.com>

security/yama/yama_lsm.c

@@ -485,6 +485,6 @@ static inline void yama_init_sysctl(void) { }
 void __init yama_add_hooks(void)
 {
 	pr_info("Yama: becoming mindful.\n");
-	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks));
+	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
 	yama_init_sysctl();
 }