nfp: register devlink after app is created

Devlink used to have two global locks: devlink lock and port lock,
our lock ordering looked like this:

  devlink lock -> driver's pf->lock -> devlink port lock

After recent changes port lock was replaced with per-instance
lock.  Unfortunately, new per-instance lock is taken on most
operations now.  This means we can only grab the pf->lock from
the port split/unsplit ops.  Lock ordering looks like this:

  devlink lock -> driver's pf->lock -> devlink instance lock

Since we can't take pf->lock from most devlink ops, make sure
nfp_apps are prepared to service them as soon as devlink is
registered.  Locking the pf must be pushed down after
nfp_app_init() callback.

The init order looks like this:
 nfp_app_init
 devlink_register
 nfp_app_start
 netdev/port_register

As soon as app_init is done nfp_apps must be ready to service
devlink-related callbacks.  apps can only register their own
devlink objects from nfp_app_start.

Fixes: 2406e7e5 ("devlink: Add per devlink instance lock")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>