dt-bindings: hwmon: add compatible for max1619

Add new device tree bindings document for max1619 device
including a new compatible string.

Signed-off-by: Alan Tull <atull@kernel.org>
Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>