nfp: map mac_stats and vf_cfg BARs

If present map mac_stats and vf_cfg BARs. These will be used by
representor netdevs to read statistics for phys port and vf representors.

Also provide defines describing the layout of the mac_stats area.
Similar defines are already present for the cf_cfg area.

Based in part on work by Jakub Kicinski.

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