dt-bindings: mfd: gateworks-gsc: Add 16bit pre-scaled voltage mode

Add a 16-bit pre-scaled voltage mode to ADC and clarify that existing
pre-scaled mode is 24bit.
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/gateworks-gsc.yaml

@@ -79,11 +79,12 @@ properties:
             description: |
               conversion mode:
                 0 - temperature, in C*10
-                1 - pre-scaled voltage value
+                1 - pre-scaled 24-bit voltage value
                 2 - scaled voltage based on an optional resistor divider
                     and optional offset
+                3 - pre-scaled 16-bit voltage value
             $ref: /schemas/types.yaml#/definitions/uint32
-            enum: [0, 1, 2]
+            enum: [0, 1, 2, 3]
 
           gw,voltage-divider-ohms:
             description: Values of resistors for divider on raw ADC input