README says :
---
4. Boot Instructions
====================
You must load the DTB (device tree blob) into the target's memory
prior to booting the kernel Image. The DTB file can be found in the export
directory after building a project, or you can generate it manually with the
following commands:
# bitbake -c devshell virtual/kernel
# make zynqmp-<Board Name>.dtb
---
Correct command is :
make zynqmp-<Board Name>.dtb
Also it would be helpful to mention where we can retrieve the different supported <Board Name> :
--> ls arch/arm64/boot/dts/xilinx/
