crypto: tcrypt - enable tests for xxhash and blake2

Fill some of the recently freed up slots in tcrypt with xxhash64 and
blake2b/blake2s, so we can easily benchmark their kernel implementations
from user space.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>