mpt_sas: allow physical topology enumeration in libtopo
mpt_sas tracks an (enclosure, slot) tuple for each target which is, at least in the Richmond-A, usefully mapped to physical HBA ports. We can use these to create static mappings in libtopo between a specific mpt_sas (enclosure, slot) tuple and a drive bay. To enable this, we need:
- A Private ioctl exposing the list of known (enclosure, slot) tuples for all mpt_sas targets.
- Modifications to the disk libtopo module to allow disk nodes to be created based on a (mpt_sas devctl path, enclosure, slot) match described in a libtopo XML mapping.