nfp: split out the allocation part of open

Our open/close implementations have 3 stages:
 - allocation/freeing of ring resources, irqs etc.,
 - device config,
 - device/stack enable (can't fail).

Right now all of those stages are placed in separate functions,
apart from allocation during open.  Fix that.  It will make it
easier for us to allocate resources for netdev-less vNICs.
Because we want to reuse allocation code in netdev-less vNICs
leave the netif_set_real_num_[rt]x_queues() calls inside open.

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