Boxes without IPMI (Dell workstations like dev-linux) expose CPU/ambient/
SODIMM/board temps via the BIOS SMM interface (dell_smm hwmon). Add
read_hwmon_env(): labelled temps from chips in HOST_HWMON_CHIPS (default
'dell_smm') as env sensors, named '<chip> <label>' with index suffix for
repeated labels. Merged into the host-poller env sweep. No-op on hosts without
the configured chips.