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/procattr.c

@@ -15,6 +15,7 @@
 #include "include/apparmor.h"
 #include "include/context.h"
 #include "include/policy.h"
+#include "include/policy_ns.h"
 #include "include/domain.h"
 #include "include/procattr.h"