crypto: af_alg - Allow cbc(paes)

Commit 7524070f26d8 ("crypto: af_alg - Drop support for off-CPU cryptography")
breaks a special use case.  The cbc-paes-caam driver implements the
algorithm cbc(paes), it offers a way to use AES in CBC mode with key
material unknown to userspace.  Instead of an AES key a CAAM BLOB is
passed to the kernel.  So, this crypto operation cannot be
implemented in a userspace library and needs always help from the
kernel.

Explicitly allow this use case.

Cc: Demi Marie Obenour <demiobenour@gmail.com>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Fixes: 7524070f26d8 ("crypto: af_alg - Drop support for off-CPU cryptography")
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>