There are a few differences, but the one we're interested in is
that PCIe Root Ports are finally available: as a result of this,
our riscv64-virt-headless guest will switch from virtio-mmio to
virtio-pci.
Signed-off-by: Andrea Bolognani <abologna@redhat.com> Reviewed-by: Cole Robinson <crobinso@redhat.com>