The guilty commit is following. I reverted this commit on top of the current amd-staging-drm-next (40cc64619a2580b26f924bcabdefd555e7831a14), my system is then booting ok. It seems to do some specific programming for vega10+ parts which is not correct for previous families/versions parts.

commit 43ee614432d841184b158af27fda66a0929fe252 (refs/bisect/bad)
Author: Emily Deng <Emily.Deng@amd.com>
Date:   Tue May 28 10:17:04 2019 +0800

    drm/amdgpu: Need to set the baco cap before baco reset

    For passthrough, after rebooted the VM, driver will do
    a baco reset before doing other driver initialization during loading
     driver. For doing the baco reset, it will first
    check the baco reset capability. So first need to set the
    cap from the vbios information or baco reset won't be
    enabled.

    Signed-off-by: Emily Deng <Emily.Deng@amd.com>
    Reviewed-by: Evan Quan <evan.quan@amd.com>

Created attachment 144429 [details]
dmesg

Created attachment 144430 [details]
xorg

Created attachment 144570 [details] [review]
possible fix

Does this patch help?

Did update the amd-staging-drm-next branch earlier today. The hanging boot is
gone. Did a quick check: your patch was already applied. So it probably did fix
it.