hwmon: Add Nuvoton NCT7904 hwmon driver

The NCT7904D is a hardware monitor supporting up to 20 voltage sensors,
internal temperature sensor, Intel PECI and AMD SB-TSI CPU temperature
interface, up to 12 fan tachometer inputs, up to 4 fan control channels
with SmartFan.

Signed-off-by: Vadim V. Vlasov <vvlasov@dev.rtsoft.ru>
[Guenter Roeck: Fixed whitespace errors, dropped redundant comment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>