dt-bindings: iio: adc: add input-chopping property

Add a generic input-chopping property to adc.yaml. This is a feature
seen frequently in ADCs that are designed to measure resistive loads,
such as RTDs and strain gauges. Enabling this can reduce offset errors
by swapping the positive and negative input channels on every other
conversion. This can have side-effects in timing and filter response, so
it is not always desirable to enable this feature in some applications.
Therefore, it is best to make this a property that can be enabled or
disabled in the device tree.

Signed-off-by: David Lechner (TI) <dlechner@baylibre.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

Documentation/devicetree/bindings/iio/adc/adc.yaml

@@ -80,6 +80,14 @@ properties:
       ADCs usually allow choosing between internal reference sources or a pair
       of external pins.
 
+  input-chopping:
+    type: boolean
+    description:
+      If set, the positive and negative input channels are swapped on every
+      other conversion to reduce offset error. This generally comes at the
+      expense of added settling time between conversions, so should be omitted
+      on systems with high-frequency signals or high data rate requirements.
+
   excitation-channels:
     $ref: /schemas/types.yaml#/definitions/uint32-array
     description: