nfp: separate app vNIC init/clean from alloc/free

We currently only have one app callback for vNIC creation
and destruction.  This is insufficient, because some actions
have to be taken before netdev is registered, after it's
registered and after it's unregistered.  Old callbacks
were really corresponding to alloc/free actions.  Rename
them and add proper init/clean.  Apps using representors
will be able to use new callbacks to manage lifetime of
upper devices.

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>