I have a PC with:
MB: Asrock AM1B-ITX
CPU: AMD Kabini Athlon 5350 APU
iGPU: Radeon HD 8400 / R3 Series
Displays: DVI Asus, HDMI Samsung

Kernels: 4.12/4.14/4.15/4.16/4.17
Drivers: radeon, amdgpu, amdgpu-dc

Booting in UEFI mode, EFIFB/SimpleFB

When the drm driver is loaded on system boot or when is loaded manually the
screen goes blank. The screen content reappears after the driver has been
loaded.
I assume switching from efifb/simblefb to radeon/amdgpudrmfb causes this.