cryptodev: separate key exchange operation enum

cryptodev: separate key exchange operation enum

- Separated key exchange enum from asym op type.
Key exchange and asymmetric crypto operations like signatures,
encryption/decryption should not share same operation enum as
its use cases are unrelated and mutually exclusive.
Therefore op_type was separate into:
1) operation type
2) key exchange operation type

Signed-off-by: Arek Kusztal <arkadiuszx.kusztal@intel.com>
Acked-by: Fan Zhang <roy.fan.zhang@intel.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>