I copied the complete bootfolder incl. overlay folder to my mount and then flashed it. For me the spamming was gone and I am was able to login once to the manjaro arm os. But as I said, I had many cpu panics.
Currently I try only to copy the bcm27 files, the first try failed. I saw only the rainbow Screen the whole time.
(INFO I use a Raspberry PI 3 b, so that we know about which device we are talking :D)
Update#1:
Second try: Now I copied the firmwares only; without removing the other onces from the .img and I get the spamming error again. Next try 
Update#2:
ITS WORKING!
What I did:
First I downloaded a fresh .img from Manjaro ARM on main-site (http://manjaro-arm.org/downloads.php) and the complete firmware source (Master Brunch) from the official raspberryGithub (https://github.com/raspberrypi/firmware/tree/master/boot).
Then I mounted the .img with and deleted the complete overlays folder. Then I copied the complete overlays folder from the brunch to the mounted img.
Files from the /boot folder I copied:
- all .dtb files
- the start_xxx files (4files, i think they were up-to-date, just in case copied them)
- and the fixup_xxx files (4files as well) I think this are the important once!!!
If someone is new to linux and have questions how to mount the manjaro img with the offsets, feel free to ask me.
Update#3:
After running: sudo pacman -Syu and reboot, the system is still running \o/!