dt-bindings: gpu: samsung-g2d: constrain iommus and power-domains

Provide specific constraints for iommus and power-domains, based on
current DTS.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/gpu/samsung-g2d.yaml

···
     minItems: 1
     maxItems: 2
 
-  iommus: {}
-  power-domains: {}
+  iommus:
+    minItems: 1
+    maxItems: 2
+
+  power-domains:
+    maxItems: 1
 
 required:
   - compatible