Ok, I found the solution!
First, drm_kms_helper.edid_firmware becomes drm.edid_firmware.
Second, the syntax of the video param is now video=HDMI-A-1:1280x720@60D instead of video=HDMI-A-1:1280x720@60:D. No more : before D. Grrr!
Then, I had to generate 2 edid.bin files, one for the monitor, one for the projector. When using the monitor edid.bin file for the projector, the projector timings where wrong (it worked fine previously). So, the entire solution is:
# mkdir -p /storage/.config/firmware/edid
# cat /sys/class/drm/card0-HDMI-A-1/edid > /storage/.config/firmware/edid/projo_edid.bin
# cat /sys/class/drm/card0-HDMI-A-2/edid > /storage/.config/firmware/edid/monitor_edid.bin
# cd ~
# mkdir -p cpio/lib/firmware/edid
# cp .config/firmware/edid/* cpio/lib/firmware/edid/
# cd cpio/
# find . -print | cpio -ov -H newc > ../edid.cpio
# mount -o remount,rw /flash
# mv ../edid.cpio /flash/
# nano /flash/extlinux.conf
on the kernel command line, add:
initrd=/edid.cpio drm.edid_firmware=HDMI-A-1:edid/projo_edid.bin,HDMI-A-2:edid/monitor_edid.bin video=HDMI-A-1:1280x720@60D video=HDMI-A-2:1280x720@60D
And finally:
# cd /lib/firmware/edid/
# ln -s /storage/.config/firmware/edid/monitor_edid.bin monitor_edid.bin
# ln -s /storage/.config/firmware/edid/projo_edid.bin projo_edid.bin
# reboot
Hope this helps!