net: dsa: sja1105: populate supported_interfaces

Populate the supported interfaces bitmap for the SJA1105 DSA switch.

This switch only supports a static model of configuration, so we
restrict the interface modes to the configured setting.

Reviewed-by: Vladimir Oltean &lt;olteanv@gmail.com&gt; Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: Vladimir Oltean <vladimir.    │
Signed-off-by: David S. Miller <davem@davemloft.net>