Sorry, I thought this was clear. This issue is the UEFI config not matching your dtb name. If you need to have a different dtb name, then you have to change the UEFI config, although this will mean that Linaro generated test images no longer work.

You say you built an image with the correctly named dtb. Have you taken a look on the sd card testboot partition to see if it really is there?

Thanks

Dave