crypto: speck - add test vectors for Speck64-XTS

Add test vectors for Speck64-XTS, generated in userspace using C code.
The inputs were borrowed from the AES-XTS test vectors, with key lengths
adjusted.

xts-speck64-neon passes these tests.  However, they aren't currently
applicable for the generic XTS template, as that only supports a 128-bit
block size.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>