dpaa2-eth: Rename structure

Since the array of supported header fields will be used for
Rx flow classification as well, rename it from "hash_fields" to
the more inclusive "dist_fields".

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