doc: security: Add kern-doc for lsm_hooks.h

There is a lot of kern-doc for the LSM internals, but it wasn't visible
in the HTML output. This exposes some formatting flaws in lsm_hooks.h
that will be fixed in a later series of patches.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/security/LSM.rst

@@ -11,4 +11,7 @@ that end users and distros can make a more informed decision about which
 LSMs suit their requirements.
 
 For extensive documentation on the available LSM hook interfaces, please
-see ``include/linux/lsm_hooks.h``.
+see ``include/linux/lsm_hooks.h`` and associated structures:
+
+.. kernel-doc:: include/linux/lsm_hooks.h
+   :internal: