platform/x86: dell-ddv: Add hwmon support

platform/x86: dell-ddv: Add hwmon support

Thanks to bugreport 216655 on bugzilla triggered by the
dell-smm-hwmon driver, the contents of the sensor buffers
could be almost completely decoded.
Add an hwmon interface for exposing the fan and thermal
sensor values. Since the WMI interface can be quite slow
on some machines, the sensor buffers are cached for 1 second
to lessen the performance impact.
The debugfs interface remains in place to aid in reverse-engineering
of unknown sensor types and the thermal buffer.

Tested-by: Antonín Skala <skala.antonin@gmail.com>
Tested-by: Gustavo Walbon <gustavowalbon@gmail.com>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230209211503.2739-2-W_Armin@gmx.de
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>