hwmon: Add KEBA battery monitoring controller support

hwmon: Add KEBA battery monitoring controller support

The KEBA battery monitoring controller is found in the system FPGA of
KEBA PLC devices. It puts a load on the coin cell battery to check the
state of the battery. If the coin cell battery is nearly empty, then
the user space is signaled with a hwmon alarm.

The auxiliary device for this driver is instantiated by the cp500 misc
driver.

Signed-off-by: Gerhard Engleder <eg@keba.com>
Link: https://lore.kernel.org/r/20250409190830.60489-1-gerhard@engleder-embedded.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>