4 - compatible: Must be one of the following:
5 - "microchip,mcp3021" for mcp3021
6 - "microchip,mcp3221" for mcp3221
11 - reference-voltage-microvolt
12 Reference voltage in microvolt (uV)
17 compatible = "microchip,mcp3021";
20 reference-voltage-microvolt = <4500000>; /* 4.5 V */