drivers: hwmon: add driver for max42500

The driver implementation is revised to follow the hwmon ABI for all
sysfs attributes. Additionally, two gpio pins for EN0 and EN1 ports
have been implemented for optional control of power source and trigger
the FPSR to record the power-up or power-down timestamps.

Signed-off-by: Kent Libetario <[email protected]>

Author: kentlibe