crypto: s390 - add System z hardware support for XTS mode

This patch adds System z hardware acceleration support for the AES XTS mode.
The hardware support is available beginning with System z196.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>