Add virtio-mmio support (VirtioMmioDeviceLib and VirtioFdtDxe).
With this patch added and a new enough qemu version (6.2+) edk2
will detect virtio-mmio devices, so it is possible to boot from
storage (virtio-blk, virtio-scsi) or network (virtio-net).
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3689 Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>