Comment # 2 on bug 102497 from Mikulas Patocka

U-BOOT initializes the PCIe controller with 16MB window - it's too small for
GPUs. You have to compile the EDK EFI firmware. You don't have to flash it, you
can copy flash-image.bin to sdcard starting at sector 4096 and use the switches
on the board to select boot from sdcard.

I've got GPU working this way, but opengl doesn't work because of glitches when
writing to the framebuffer.