dt-binding: hwmon: Add documentation for ADM1177

Documentation for ADM1177 was added.

Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200114112159.25998-2-beniamin.bia@analog.com


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