dt-bindings: iio: light: veml6075: document vishay,rset-ohms

The veml6070 provides a configurable integration time by means of an
external resistor (Rset in the datasheet) with values between 75 and
1200 kohms.

Document vishay,rset-ohms to select the integration time.

Signed-off-by: Javier Carrasco <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/light/vishay,veml6075.yaml

···
   reg:
     maxItems: 1
 
+  vishay,rset-ohms:
+    description:
+      Resistor used to select the integration time.
+    default: 270000
+    minimum: 75000
+    maximum: 1200000
+
   vdd-supply: true
 
 required:
   - compatible
   - reg
   - vdd-supply
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          enum:
+            - vishay,veml6040
+            - vishay,veml6075
+    then:
+      properties:
+        vishay,rset-ohms: false
 
 additionalProperties: false