crypto: x86/aesni - Perform address alignment early for XTS mode

Currently, the alignment of each field in struct aesni_xts_ctx occurs
right before every access. However, it's possible to perform this
alignment ahead of time.

Introduce a helper function that converts struct crypto_skcipher *tfm
to struct aesni_xts_ctx *ctx and returns an aligned address. Utilize
this helper function at the beginning of each XTS function and then
eliminate redundant alignment code.

Suggested-by: Eric Biggers <ebiggers@kernel.org>
Link: https://lore.kernel.org/all/ZFWQ4sZEVu%2FLHq+Q@gmail.com/


Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: linux-crypto@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>