nfp: implement ethtool get module EEPROM

Now that the NSP provides the ability to read from the SFF modules'
EEPROM, we can use this interface to implement the ethtool callback.

If the NSP only provides partial data, we log the event from within
the driver but pass a success code to ethtool to prevent it from
discarding the partial data.

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