MFC r340425 (by cem): amdsmn(4)/amdtemp(4): Attach to Ryzen 2 hostbridges

As reported, tested, and patch supplied by Johannes.

There may be future work to do to support multiple sensors, but for now, any
sensor at all is a strict improvement for Ryzen 2 systems.

PR: 228480
Submitted by: Johannes Lundberg <johalun0 AT gmail.com> (earlier version)
Reported by: deischen@, Johannes, and numerous others