Convert the AVX and AVX2 implementations of Serpent from the
(deprecated) ablkcipher and blkcipher interfaces over to the skcipher
interface.  Note that this includes replacing the use of ablk_helper
with crypto_simd.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>