crypto: serpent-sse2 - select LRW and XTS

serpent-sse2 uses functions from LRW and XTS modules, so selecting would appear
to be better option than using #ifdefs in serpent_sse2_glue.c to enable/disable
LRW and XTS features.

This also fixes build problem when serpent-sse2 would be build into kernel but
XTS/LRW are build as modules.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>