apparmor: split apparmor policy namespaces code into its own file

Policy namespaces will be diverging from profile management and
expanding so put it in its own file.

Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/apparmorfs.c

@@ -28,6 +28,7 @@
 #include "include/context.h"
 #include "include/crypto.h"
 #include "include/policy.h"
+#include "include/policy_ns.h"
 #include "include/resource.h"
 
 /**