It is a legacy PCI device like all the other sound devices, but there is an exception in libvirt that assigns it to the standard location of 00:1B.0 (on the root bus), which is where that device is located on real Q35 hardware. The result will be (again) that libvirt doesn't have to pull in a legacy PCI bridge.
Re-targeting to 4.3.1 since it is missing a patch, an acked blocker flag, or both
done in commit 6cfa1d80c48d26e5a83c9d3535b13cfdf7649ec7 already a year ago. Will be in 4.3