dt-bindings: hwmon: Add Atmel AT30TS74

Document the Atmel (now Microchip) AT30TS74 which is an LM75 based
temperature sensor.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/9c01b1b5-871a-2b34-9f98-766d043e0759@axentia.se


Signed-off-by: Guenter Roeck <linux@roeck-us.net>