arm64: dts: ls1046a-qds: add mmio based mdio-mux nodes for FPGA

There is mmio based mdio mux function in the FPGA device on ls1046a-qds
board.  Add the mmio based mdio-mux nodes to ls1043a-qds boards and
add simple-mfd as a compatbile for the FPGA node to reflect the
multi-function nature of it.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Pankaj Bansal <pankaj.bansal@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>