sled-agent should use libtopo more (or at all!)

Currently, sled-agent detects disks via libdevinfo as described in RFD 352, which also describes this as an expediency decision: this limits sled-agent to handling disks that are all of: physically present, powered, with a driver attached. If anything on the path to attaching a driver goes wrong, sled-agent just won't see the disk anymore. When we change this, we should remember to update RFD 352 to match.

I am imminently adding CPU family detection logic to sled-agent, which duplicates the same detection done in the kernel. A really disappointing solution would be to use libtopo and match on the revision of GN-B1 or whatever to CPU families, a better solution would be to enhance libtopo to include the CPU family and uarch identified by the kernel, but both solutions involve "use libtopo to collect a topology snapshot and walk it for details you need".

In both cases our lives would be a little better if we used libtopo, so we ought to one day.

Start by reading RFD 352 and the existing sled-agent disk detection that uses libdevinfo. Review the libtopo topology-snapshot approach described in the issue and the CPU-family work in PR 8725. Before implementation, define which disk and CPU details libtopo must provide; done should include updating RFD 352 to match the new behavior.