dpaa2-eth: Update hash key composition code

Introduce an internal id bitfield to uniquely identify header fields
supported by the Rx distribution keys. For the hash key, add a
conversion from the RXH_* bitmask provided by ethtool to the internal
ids.

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