Convert the AVX implementation of CAST6 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: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>