nfp: report MAC statistics in ethtool

Add reporting of MAC statistics in ethtool.  MAC statistics
are read out from the MAC IP and accumulated by application
FW, therefore their presence depends on the application FW.

Add missing defines and string names for the statistics and
dump them in ethtool -S.

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>