arm64: dts: ls208xa-qds: add mdio mux nodes from on-board FPGA

Update the cpld node name to be generic board-contrl and add mmio mdio
mux nodes from the on-board FPGA.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>