mlxsw: Make devlink port instances independent of spectrum/switchx2 port instances

Currently, devlink register/unregister is done directly from
spectrum/switchx2 port create/remove functions. With a need to
introduce a port type change, the devlink port instances have to be
persistent across type changes, therefore across port create/remove
function calls. So do a bit of reshuffling to achieve that.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Elad Raz <eladr@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>