cryptodev: remove digest length from crypto op

cryptodev: remove digest length from crypto op

Digest length was duplicated in the authentication transform
and the crypto operation structures.

Since digest length is not expected to change in a same
session, it is removed from the crypto operation.

Also, the length has been shrunk to 16 bits,
which should be sufficient for any digest.

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>
Acked-by: Fiona Trahe <fiona.trahe@intel.com>