dt-bindings: net: Add bindings for mdio mux consumers

When we use the bindings defined in Documentation/devicetree/bindings/mux
to define mdio mux in producer and consumer terms, it results in two
devices. one is mux producer and other is mux consumer.

Add the bindings needed for Mdio mux consumer devices.

Signed-off-by: Pankaj Bansal <pankaj.bansal@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>