Even with the new u-boot version provided in comment #13, the dtb file configured by the FDT entry in extlinux.conf is not loaded correctly. So the bug is still there. At the moment, with the help of
- the patch at Jetpack-4.5.1 silent panic when booting, with kernel patch
- the tool to sign a dtb file locally at Request for a tool to update device tree locally. - #22 by bondar99
I can get around the problem.
But, as I wrote above, the bug in loading the FDT chosen in extlinux.conf if it is different from the dtb stored in the kernel-dtb partition, that bug is still present with the last version of uboot I was asked to test.