`grub-install` fails to install properly when run on a system using
U-Boot's implementation of the EFI protocol (potentially also effects
package grub-efi-arm64, perhaps this should be against src:grub2).

Since a Tianocore-based implementation of the EFI protocol is also
available, I can provide more imformation.  A useful distinction is
U-Boot's EFI implementation does NOT implement EFI variables.  This seems
a plausible method to distinguish U-Boot's partial EFI implementation
from Tianocore's complete EFI implementation.

On the U-Boot implementation grubaa64.efi needs to be installed as
/boot/efi/EFI/BOOT/bootaa64.efi instead.  Roughly akin to
--bootloader-id=BOOT, plus an extra rename.  I suspect I may be filing
other bugs soon.

(the platform is a Raspberry Pi 4B, the Tianocore implementation is
quite workable except too many pieces of software assume device-tree
on ARM and won't work with ACPI)