nfp: abm: look up MAC addresses via management FW

In multi-host scenarios Management FW may allocate MAC addresses
at runtime, we have to use the indirect lookup to find them.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>