Default machine setting of force-legacy=true causes problems for any modern VirtIO device using MMIO
Description of problem:
The default causes problems if you enable any non-legacy VirtIO device which has the VIRTIO_F_VERSION_1 feature bit will not properly read all feature bits. This is because reading VIRTIO_MMIO_VERSION returns VIRT_VERSION_LEGACY which in turn results in the driver not reading all feature bits, e.g. the qtest access:

```
static uint64_t qvirtio_mmio_get_features(QVirtioDevice *d)
{
    QVirtioMMIODevice *dev = container_of(d, QVirtioMMIODevice, vdev);
    uint64_t lo;
    uint64_t hi = 0;

    qtest_writel(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES_SEL, 0);
    lo = qtest_readl(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES);

    if (dev->version >= 2) {
        qtest_writel(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES_SEL, 1);
        hi = qtest_readl(dev->qts, dev->addr + QVIRTIO_MMIO_HOST_FEATURES);
    }

    return (hi << 32) | lo;
}
```
Additional information: