I had a weird bug with my Radeon 5770 where OVMF would display either a black screen or totally garbage output if I had less than 2 GiB in the VM. You're using just 1, try with 2. Try also with Chipset Q35 instead of 440FX (-M q35).
Also, for correctness sake, add a PCIe Root Port and attach the card to it:
-device ioh3420,chassis=0,id=pcie.1 \
-device vfio-pci,host=01:00.0,multifunction=true,bus=pcie.1,addr=00.0 \
-device vfio-pci,host=01:00.1,bus=pcie.1,addr=00.1 \