crypto: cipher - remove crt_u.cipher (struct cipher_tfm)

crypto: cipher - remove crt_u.cipher (struct cipher_tfm)

Of the three fields in crt_u.cipher (struct cipher_tfm), ->cit_setkey()
is pointless because it always points to setkey() in crypto/cipher.c.

->cit_decrypt_one() and ->cit_encrypt_one() are slightly less pointless,
since if the algorithm doesn't have an alignmask, they are set directly
to ->cia_encrypt() and ->cia_decrypt().  However, this "optimization"
isn't worthwhile because:

- The "cipher" algorithm type is the only algorithm still using crt_u,
  so it's bloating every struct crypto_tfm for every algorithm type.

- If the algorithm has an alignmask, this "optimization" actually makes
  things slower, as it causes 2 indirect calls per block rather than 1.

- It adds extra code complexity.

- Some templates already call ->cia_encrypt()/->cia_decrypt() directly
  instead of going through ->cit_encrypt_one()/->cit_decrypt_one().

- The "cipher" algorithm type never gives optimal performance anyway.
  For that, a higher-level type such as skcipher needs to be used.

Therefore, just remove the extra indirection, and make
crypto_cipher_setkey(), crypto_cipher_encrypt_one(), and
crypto_cipher_decrypt_one() be direct calls into crypto/cipher.c.

Also remove the unused function crypto_cipher_cast().

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