ARM: dts: NSP: Provide defaults ports container node

Provide an empty 'ports' container node with the correct #address-cells
and #size-cells properties. This silences the following warning:

arch/arm/boot/dts/bcm958522er.dt.yaml:
ethernet-switch@36000: 'oneOf' conditional failed, one must be fixed:
            'ports' is a required property
            'ethernet-ports' is a required property
            From schema:
Documentation/devicetree/bindings/net/dsa/b53.yaml

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>