crypto: move QCryptoHashAlgorithm enum definition into QAPI

The QCryptoHashAlgorithm enum is defined in the crypto/hash.h
header. In the future some QAPI types will want to reference
the hash enums, so move the enum definition into QAPI too.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>