crypto: atmel-aes - add support to the XTS mode

This patch adds the xts(aes) algorithm, which is supported from
hardware version 0x500 and above (sama5d2x).

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>