dt-bindings: iio: adc: Add binding for ADC on pms405 PMIC

PMS405 contains a variant of the spmi-adc-rev2 ADC. Create a new
compatible inorder to handle any differences.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>

Documentation/devicetree/bindings/iio/adc/qcom,spmi-vadc.txt

@@ -13,6 +13,7 @@ VADC node:
     Definition: Should contain "qcom,spmi-vadc".
                 Should contain "qcom,spmi-adc5" for PMIC5 ADC driver.
                 Should contain "qcom,spmi-adc-rev2" for PMIC rev2 ADC driver.
+                Should contain "qcom,pms405-adc" for PMS405 PMIC
 
 - reg:
     Usage: required