TOMOYO: Fix make namespacecheck warnings.

Commit efe836ab "TOMOYO: Add built-in policy support." introduced
tomoyo_load_builtin_policy() but was by error called from nowhere.

Commit b22b8b9f "TOMOYO: Rename meminfo to stat and show more statistics."
introduced tomoyo_update_stat() but was by error not called from
tomoyo_assign_domain().

Also, mark tomoyo_io_printf() and tomoyo_path_permission() static functions,
as reported by "make namespacecheck".

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>