yes, indeed I see both ethernet addresses showing up with mdio list command. Can you try to modify your device tree to include the new .dts modification one I posted here Enabling second ethernet connection to a fully hardware configured switch IC - #4 by andi.tx?
I did some mistakes with the first suggestion. @KDehren could confirm that it works with overlay. (EDIT: it hasn’t worked yet, but still I suggest you try it in your .dts)
I understood that you change the device tree for U-Boot? Do you need the switch to be available in U-Boot already? Your changes in the U-Boot device tree won’t be passed to the Linux Kernel