crypto: xor - Check for osxsave as well as avx in crypto/xor

This affects xen pv guests with sufficiently old versions of xen and
sufficiently new hardware.  On such a system, a guest with a btrfs
root won't even boot.

Signed-off-by: John Haxby <john.haxby@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>