platform/x86: simatic-ipc: add CMOS battery monitoring

platform/x86: simatic-ipc: add CMOS battery monitoring

Siemens Simatic Industrial PCs can monitor the voltage of the CMOS
battery with two bits that indicate low or empty state. This can be GPIO
or PortIO based.
Here we model that as a hwmon voltage. The core driver does the PortIO
and provides boilerplate for the GPIO versions. Which are split out to
model runtime dependencies while allowing fine-grained kernel
configuration.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230706154831.19100-3-henning.schild@siemens.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>