crypto: x86/aes-xts - make non-AVX implementation use new glue code

Make the non-AVX implementation of AES-XTS (xts-aes-aesni) use the new
glue code that was introduced for the AVX implementations of AES-XTS.
This reduces code size, and it improves the performance of xts-aes-aesni
due to the optimization for messages that don't span page boundaries.

This required moving the new glue functions higher up in the file and
allowing the IV encryption function to be specified by the caller.

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