soft-npu: need means of self-identification #234
Description
Right now when you launch a VM with soft-npu the only way you know that this is present is by opening up the right UART and sending a message. When we look at trying to fit that together with the general detection methods of a scrimlet, that's not really a good strategy. We really shouldn't be going around assuming UARTs are or aren't something. It'd be much more helpful to have a self-identifying means of this. One way to do this would be to have a dummy PCI device that shows up as revision 0 and has no BARs, only a set PCI ID. If we did later move the UART interface to this, we would then change the hardware revision and use that in the compatible array as part of attaching.
There are other ways like custom smbios tables or more, but the PCI device seems like the thing that's most up our alley.