dt-bindings: net: fec: add iommus property

iMX8QM have iommu. Add proerty 'iommus'.
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240201-8qm_smmu-v2-2-3d12a80201a3@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/fsl,fec.yaml

@@ -224,6 +224,9 @@ properties:
       Can be omitted thus no delay is observed. Delay is in range of 1ms to 1000ms.
       Other delays are invalid.
 
+  iommus:
+    maxItems: 1
+
 required:
   - compatible
   - reg