crypto: x86/serpent-avx,avx2 - convert to skcipher interface

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: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>