dt-bindings: i2c: nvidia,tegra20-i2c: define power-domains top-level

Properties are expected to be defined in top-level "properties:" block
and further customized in "if:then:".  Only one variant has power
domains, so add respective top-level property and disallow it for other
devices.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

Documentation/devicetree/bindings/i2c/nvidia,tegra20-i2c.yaml

@@ -103,6 +103,9 @@ properties:
     items:
       - const: i2c
 
+  power-domains:
+    maxItems: 1
+
   dmas:
     items:
       - description: DMA channel for the reception FIFO
@@ -162,6 +165,9 @@ allOf:
         power-domains:
           items:
             - description: phandle to the VENC power domain
+    else:
+      properties:
+        power-domains: false
 
 unevaluatedProperties: false