dt-bindings: i2c: Add P8 OCC hwmon device documentation

Device-tree bindings for I2C-based On-Chip Controller hwmon device

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Required properties:

 - compatible = "ibm,p8-occ-hwmon";

 - reg = <I2C address>;			: I2C bus address

Examples:

    i2c-bus@100 {

        #address-cells = <1>;

        #size-cells = <0>;

        clock-frequency = <100000>;

        < more properties >

        occ-hwmon@1 {

            compatible = "ibm,p8-occ-hwmon";

            reg = <0x50>;

        };

        occ-hwmon@2 {

            compatible = "ibm,p8-occ-hwmon";

            reg = <0x51>;

        };

    };