I have reinstalled grub-efi-arm 2.02+dfsg1-9.
With my current U-Boot and a custom built the 4.18.20 kernel I am able
to boot.
The stock Debian kernel does not boot.
What it takes is a U-Boot v2018.11 with these additional patches:
* Revert "efi_loader: remove efi_exit_caches()"
* efi_loader: Ensure memory allocations are page aligned
* lib: crc32: mark static variable as __efi_runtime_data
(not relevant for Tinker Board)
and a kernel with Ard's patch
43b2ceb0d4e0147b114cb1d0112a988cbb81ecbc
efi/arm: Revert deferred unmap of early memmap mapping
This patch is available since Linux v4.19.6.
Best regards
Heinrich