OK, my fault. I tried it some time ago and forgot details. I tried it again and indeed the device constantly reboots. Here is full log of serial console in this state. There is place where one can "Press any key for interactive startup" to get into initfs shell and avoid rebooting.

Not necessarily but it will make things simpler indeed. One variant of CA-42 cable from ebay will do.

Or you can hack kernel to let the framebuffer initialize without panel being present. Or you can flash custom rootfs with the rebooting stuff disabled.