hwmon: add driver for Microchip TC74

Add hwmon driver for the Microchip TC74.

The TC74 is a single-input 8-bit I2C temperature sensor,
with +-2 degrees centigrade accuracy.

Signed-off-by: Maciej Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>