crypto: af_alg - add user space interface for AEAD

AEAD requires the caller to specify the following information separate
from the data stream. This information allows the AEAD interface handler
to identify the AAD, ciphertext/plaintext and the authentication tag:

        * Associated authentication data of arbitrary length and
          length

        * Length of authentication tag for encryption

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>