dt-bindings: arm: fsl: add ls1021a-iot board

Add the board ls1021a-iot in the binding docuemnt.
Signed-off-by: Changming Huang <jerry.huang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -1065,6 +1065,7 @@ properties:
       - description: LS1021A based Boards
         items:
           - enum:
+              - fsl,ls1021a-iot
               - fsl,ls1021a-moxa-uc-8410a
               - fsl,ls1021a-qds
               - fsl,ls1021a-tsn