In the board/pc directory there is a file grub-efi.cfg that the readme.txt file says is used when building an EFI based image but it doesn't appear that the grub configuration from that file is ever used any place. Instead, the script post-image-efi-gpt.sh has a grub configuration embedded in it that gets used.
Thanks for the report, you're totally right. I have submitted http://patchwork.ozlabs.org/patch/1097871/ to fix this.
Fix has now been committed, thanks