Pin down initial SMB OS image and initial ics_xcu_SMB tag

The new temperature/heater boards run on Raspberry Pis, so need a boot image, one which works for PFS, has ssh, etc. The one on n8 is I think the last and thus cleanest one. Grab it for Josh to install.

Likewise the SMB program. The one on n8 is running with a lean and fast loop (reads just the sensors, and no internal reference voltages, etc).