Add the device-tree structure describing the MUX in board dts. QDS board has an on-board RGMII PHY and 4 slots for extension cards. All these can be accessed over MDIO through a MDIO MUX controlled over I2C. Signed-off-by: Alex Marginean <alexm.osslist@gmail.com> Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>