Implement passive cooling.  It is enabled for tz0 by default where it is available.
Implement passive cooling.  It is enabled for tz0 by default where
it is available.

Reviewed by:	njl

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase