platform/x86: portwell-ec: Add hwmon support for voltage and temperature

platform/x86: portwell-ec: Add hwmon support for voltage and temperature

Integrates voltage and temperature monitoring into the driver via the hwmon
subsystem, enabling standardized reporting via tools like lm-sensors.

Signed-off-by: Yen-Chi Huang <jesse.huang@portwell.com.tw>
Link: https://patch.msgid.link/0d73c577-1941-44b4-917e-3aed6f1f664a@portwell.com.tw
[ij: align struct member comments]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>