dt-bindings: iio: adc: adi,ad7380: add spi-rx-bus-width property

Add spi-rx-bus-width property to describe how many SDO lines are wired
up on the ADC. These chips are simultaneous sampling ADCs and have one
SDO line per channel, either 2 or 4 total depending on the part number.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml

@@ -62,6 +62,11 @@ properties:
   spi-cpol: true
   spi-cpha: true
 
+  spi-rx-bus-width:
+    maxItems: 4
+    items:
+      maximum: 1
+
   vcc-supply:
     description: A 3V to 3.6V supply that powers the chip.
 
@@ -160,6 +165,23 @@ patternProperties:
 unevaluatedProperties: false
 
 allOf:
+  # 2-channel chips only have two SDO lines
+  - if:
+      properties:
+        compatible:
+          enum:
+            - adi,ad7380
+            - adi,ad7381
+            - adi,ad7383
+            - adi,ad7384
+            - adi,ad7386
+            - adi,ad7387
+            - adi,ad7388
+    then:
+      properties:
+        spi-rx-bus-width:
+          maxItems: 2
+
   # pseudo-differential chips require common mode voltage supplies,
   # true differential chips don't use them
   - if:
@@ -284,6 +306,7 @@ examples:
             spi-cpol;
             spi-cpha;
             spi-max-frequency = <80000000>;
+            spi-rx-bus-width = <1>, <1>, <1>, <1>;
 
             interrupts = <27 IRQ_TYPE_EDGE_FALLING>;
             interrupt-parent = <&gpio0>;