nfp: move port init to apps

Start fleshing out the apps by turning the vNIC init code to
a per-app callback.  The two initial apps we have are NIC and
eBPF.

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