There are now official debian-installer images for armhf with efikamx/sb support. Daily images are available at:
:arrow: This is a call for brave testers (with serial access to device). Report any problem and I'll try to fix it.
:!: Note it uses linux kernel from kernel.org, so video/audio/hdmi is missing, its only usable via serial console.
:idea: I'll try to build and unofficial Debian armhf image with a patched kernel, once that's available.