apparmor: rename apparmor file fns and data to indicate use

prefixes are used for fns/data that are not static to apparmorfs.c
with the prefixes being
  aafs   - special magic apparmorfs for policy namespace data
  aa_sfs - for fns/data that go into securityfs
  aa_fs  - for fns/data that may be used in the either of aafs or
           securityfs

Signed-off-by: John Johansen <john.johansen@canonical.com>
Reviewed-by: Seth Arnold <seth.arnold@canonical.com>
Reviewed-by: Kees Cook <keescook@chromium.org>