Dragonboard 410c/e geniatech with 2 GB Ram u-boot


I have a (custom?) Dragonboard 410c (or e?) with 2 GB RAM. Everythings seems okay so far, but I am using u-boot and it defaults to 1 GB RAM. I have seen, that the device tree in the kernel gets its RAM size from u-boot / bootloader?! So, my question is, does anyone know what magic keys need to get filled in the u-boot device tree to get 2 GB of RAM working?

Thanks and Regards