nfp: offload flower vxlan endpoint MAC addresses

Generate a list of MAC addresses of netdevs that could be used as VXLAN
tunnel end points. Give offloaded MACs an index for storage on the NFP in
the ranges:
0x100-0x1ff physical port representors
0x200-0x2ff VF port representors
0x300-0x3ff other offloads (e.g. vxlan netdevs, ovs bridges)

Assign phys and vf indexes based on unique 8 bit values in the port num.
Maintain list of other netdevs to ensure same netdev is not offloaded
twice and each gets a unique ID without exhausting the entries. Because
the IDs are unique but constant for a netdev, any changes are implemented
by overwriting the index on NFP.

Signed-off-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>