net: dsa: b53: Defer port enabling to calling port_enable

There is no need to configure the enabled ports once in b53_setup() and then a
second time around when dsa_switch_ops::port_enable is called, just do it when
port_enable is called which is better in terms of power consumption and
correctness.

Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>