Check out /boot/dtb/amlogic/overlay which contains some device tree overlays, including “uartA” and “uartC”. I’m not sure which one is enabled on the pins you want, respectively is attached to /dev/ttyAML1, but you can try them out.
Enable them by adding (starting with) uartA to the overlays= line in /boot/dietpiEnv.txt. No quoting or anything needed, just add an overlay right behind the = sign, or separated with a space if there is an overlay already. Generally use the filenames and remove .dtbo extension and prefix (meson- in this case).