net: dsa: move port_setup/teardown to be called outside devlink port registered area

Move port_setup() op to be called before devlink_port_register() and
port_teardown() after devlink_port_unregister().

Note it makes sense to move this alongside the rest of the devlink port
code, the reinit() function also gets much nicer, as clearly the fact that
port_setup()->devlink_port_region_create() was called in dsa_port_setup
did not fit the flow.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>