crypto: vmx - Adding asm subroutines for XTS

This patch add XTS subroutines using VMX-crypto driver.

It gives a boost of 20 times using XTS.

These code has been adopted from OpenSSL project in collaboration
with the original author (Andy Polyakov <appro@openssl.org>).

Signed-off-by: Leonidas S. Barbosa <leosilva@linux.vnet.ibm.com>
Signed-off-by: Paulo Flabiano Smorigo <pfsmorigo@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>