Move management of the superblock->sb_security blob out of the
individual security modules and into the security infrastructure.
Instead of allocating the blobs from within the modules, the modules
tell the infrastructure how much space is required, and the space is
allocated there.

Cc: John Johansen <john.johansen@canonical.com>
Signed-off-by: NCasey Schaufler <casey@schaufler-ca.com>
Signed-off-by: NMickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: NStephen Smalley <stephen.smalley.work@gmail.com>
Acked-by: NSerge Hallyn <serge@hallyn.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210422154123.13086-6-mic@digikod.netSigned-off-by: NJames Morris <jamorris@linux.microsoft.com>