nfp: make nfp_net alloc/init/cleanup/free not depend on netdevs

struct nfp_net represents a vNIC, we will be moving away from the
requirement for every vNIC to have a netdev associated with it.
Remove "netdev" from some function names and prefer passing
struct nfp_net pointer as argument instead of struct net_device *.

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>