net: sparx5: move netdev and notifier block registration to probe

net: sparx5: move netdev and notifier block registration to probe

Move netdev registration and notifier block registration from
sparx5_start() to probe(). This allows proper cleanup via goto-based
error labels in probe().

Also, remove the sparx5_cleanup_ports() helper as its functionality is now
split between sparx5_unregister_netdevs() and sparx5_destroy_netdevs()
called at appropriate points.

Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://patch.msgid.link/20260227-sparx5-init-deinit-v2-1-10ba54ccf005@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>