Allow usage of non-transitional virtio block devices (required to boot 9front)

As stated in its documentation [here](https://fqa.9front.org/fqa3.html#3.3.1.1.1), 9front requires virtio-blk-pci-non-transitional, but as far as I'm aware UTM doesn't provide any way for using that and instead defaults to virtio-blk-pci for newly added VirtIO storage devices. 9front doesn't seem to recognise these and refuses to boot.

So, as a suggestion, in this case could something like "VirtIO (non-transitional)" be provided in the Interface list under the devices?