nfp: add basic SR-IOV ndo functions to representors

Add basic ndo_set/get_vf to support SR-IOV on all types
of port representors.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
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>