nfp: calculate total port lanes for split

For port splitting we will need to know the total number of lanes
in a port.  Calculate that based on eth_table information.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>