net: dsa: b53: Disable all ports on setup

A b53 device may configured through an external EEPROM like the switch
device on the Lamobo R1 router board. The configuration of a port may
therefore differ from the reset configuration of the switch.

The switch configuration reported by the DSA subsystem is different until
the port is configured by DSA i.e. a port can be active, while the DSA
subsystem reports the port is inactive. Disable all ports and not only
the unused ones to put all ports into a well defined state.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>