net: dsa: microchip: Move *_port_setup code to dsa_switch_ops::port_setup()

Right now, the *_port_setup code is in dsa_switch_ops::port_enable(),
which is not the best place for it. This patch moves it to a more
suitable place, dsa_switch_ops::port_setup(), to match the function's
purpose and name.

This patch is a preparation for coming ACL support patch.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>