virtio: do not hard-code PCI slot IDs

[Ivan-Velickovic]

For example:

sddf/drivers/network/virtio/common/ethernet.c

Line 438 in b327f3b

dev.pci_dev = 2;

This is fragile since it depends on the hardware (or in this case, QEMU) to reliably use that number. We can setup QEMU to always use that slot but that's not 100% ideal either.

Once we have a proper PCI driver/device class we can solve this problem.

After this we can remove any mentions of addr=<addr> in virtIO arguments to QEMU.