dpaa2-eth: Configure Rx flow classification key

For firmware versions that support it, configure an Rx flow
classification key at probe time.

Hardware expects all rules in the classification table to share
the same key. So we setup a key containing all supported fields
at driver init and when a user adds classification rules through
ethtool, we will just mask out the unused header fields.

Since the key composition process is the same for flow
classification and hashing, reuse existing code where possible.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>