Patch adds XTS support for twofish-x86_64-3way by using xts_crypt(). Patch has
been tested with tcrypt and automated filesystem tests.

Tcrypt benchmarks results (twofish-3way/twofish-asm speed ratios):

Intel Celeron T1600 (fam:6, model:15, step:13):

size    xts-enc xts-dec
16B     0.98x   1.00x
64B     1.14x   1.15x
256B    1.23x   1.25x
1024B   1.26x   1.29x
8192B   1.28x   1.30x

AMD Phenom II 1055T (fam:16, model:10):

size    xts-enc xts-dec
16B     1.03x   1.03x
64B     1.13x   1.16x
256B    1.20x   1.20x
1024B   1.22x   1.22x
8192B   1.22x   1.21x
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>