dt-bindings: iio: adc: hx711: add VSUP and DVDD supply properties

Document the optional VSUP supply used by the HX711 on-chip regulator.

Also document the DVDD digital supply. DVDD is a board-supplied digital
input rail (figure 1 of the datasheet shows it as a separate supply, not
merely a bypass capacitor point) that was missing from the original
binding.

Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml

@@ -33,6 +33,19 @@ properties:
     description:
       Analog supply voltage (AVDD).
 
+  vsup-supply:
+    description:
+      Supply voltage for the on-chip regulator (VSUP).
+
+  dvdd-supply:
+    description:
+      Digital supply voltage (DVDD). On the HX711, DVDD is a
+      board-supplied digital rail; it was missing from the original
+      binding. On the HX710B, DVDD must be greater than or equal to
+      AVDD; when DVDD is a battery rail and AVDD is a regulated supply,
+      one channel monitors the DVDD-AVDD difference for battery level
+      detection.
+
   clock-frequency:
     description:
       Controls the SCK bit-bang timing. The value is used to derive the