I have been attempting this for a while. I have a 7950X but I suspect this to be a common problem for all 7000 series iGPU.
The attempt to extract vbios with UBU, amdvbflash, GPU-Z or dump from /sys/bus/pci/devices/0000:01:00.0/rom have failed.
It is very strange that this iGPU doesn't even have a rom file under /sys/bus/pci/devices/0000:01:00.0/.
On the other hand, manual hex-editing of the MoBo BIOS or dumping from /sys/kernel/debug/dri/0/amdgpu_vbios produced identical outcome rom files.
rom_parser confirms that this is a valid vBIOS, but lacks uefi compatibility.
So far I have only seen failed cases reported once every while on reddit. I have yet to see a success case.
I would wait for AGESA 1.0.0.9, which is said to provide better support for Raphael and Phoenix.