nfp: use split in naming of PCIe PF ports

PCI PFs can host more than one logical endpoint.  In NFP terms
this means having more than one vNIC for PCIe PF.  The vNICs
are usually corresponding 1:1 to Ethernet ports.  In core NIC
we use the legacy idea of vNIC *being* the Ethernet port,
hence netdevs put pX(sY) in their phys_port_name, like Ethernet
ports would.  When ASIC ports are fully represented we need to
be able to name different PCIe PF ports, too.  Use a scheme
similar to Ethernet ports - pfXsY, for PCIe PF number X,
sub-port Y.

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