mfd: arizona: Add DT binding documentation for DMIC reference voltages

    input singals. If values less than the number of input signals, elements

    that has not been specifed are set to 0 by default.

  - wlf,dmic-ref : DMIC reference voltage source for each input, can be

    selected from either MICVDD or one of the MICBIAS's, defines

    (ARIZONA_DMIC_xxxx) are provided in <dt-bindings/mfd/arizona.txt>. If

    present, the number of values should be less than or equal to the

    number of inputs, unspecified inputs will use the chip default.

  - DCVDD-supply, MICVDD-supply : Power supplies, only need to be specified if

    they are being externally supplied. As covered in

    Documentation/devicetree/bindings/regulator/regulator.txt