nfp: disallow mixing vNICs with and without NSP port entry

We only support core NIC apps which have vNICs for each physical port/
split and no representors right now.  Enforce that either each vNIC has
a NSP eth_table entry or if NSP port table is not available none do.

One scenario this will prevent from happening is user force-loading
wrong firmware file if FW app requires different firmwares per media
config.

While at it move some code to nfp_net_pf_alloc_vnic() to make it
counter-match nfp_net_pf_free_vnic() better.

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>