publicmail was asking about ACPI vs DT, not UEFI. Using UEFI and ACPI/DT are orthogonal; DT-using devices can also boot from UEFI if the firmware provides it. See https://github.com/TravMurav/dtbloader for example.
This is explicitly what we're doing in RHEL with the P550.
We use u-boot and it's EFI capabilities to init grub (instead of another instance of u-boot)
Why not use systemd-boot?
They do, Windows Phone even use UEFI (not sure was completely compliant) back in the day.
looks like they still require a custom device tree to boot Linux