Draft: vm-secure/signed-boot.bst: add rock5b devicetree
This uses the new dtbauto support in UKI and will only load if the firmware provides a devicetree compatible with this one.
Tested with EDK2 EFI firmware from https://github.com/edk2-porting/edk2-rk3588. For now, you need to configure it to provide a device tree:
Device Manager -> Rockchip Platform Configuration -> ACPI / Device Tree
and set "Config Table Mode" to "Device Tree" or "Both"