Graphical output stops with "switching to inteldrmfb from simple"

Steps to reproduce the issue: Boot kernel version 5.7.0 or later
How often does the steps listed above trigger the issue? Always.
Which platforms and features are affected (if you can). Intel Core i7-5775C integrated Iris GPU
The following information about your system:
$uname -a: Linux rigel 5.9.0-rc1-pgzh+ #1 (moved) SMP PREEMPT Sun Aug 23 13:54:13 CEST 2020 x86_64 GNU/Linux
Kernel versions 5.7.x, 5.8.x and drm-tip (5.9-rc1) are showing the issue.
Distribution: Debian 10.5
Hardware: Asus Sabertooth Z97 MK2 mainboard, Intel Core i7-5775C
Display connector: DisplayPort
Detailed description: I need to pass intel_iommu=off to the kernel cmdline to be able to boot the system, without this parameter the machine will hang in GRUB after loading kernel and initrd and does not boot. With the parameter, the graphical output stops with 'switching to inteldrmfb from simple', but I can ssh into the machine. Shutting down however does not succeed, the machine does not turn off and is not reachable via network anymore. With 5.6.x my system boots fine without any issue. *The attached logs are created with drm-tip kernel from today. *Please let me know if I can provide any other information.
/sys/class/drm/card0/error is not present.

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