@chewitt: Thank you for the info, that sounds very good (except for the slow development of the vdec driver).
First and foremost, I wanted to rule out the device-tree as an accident/non-boot source of errors for the image.
So it have been the vdec.
What is missing, I have to try it out first,
I haven't even thought of LEDs, keymaps, bluetooth, wifi, display, etc. until now.