dt-bindings: arm: imx: Add the i.MX8MN LPDDR4 EVK board

Add board binding for i.MX8MN LPDDR4 EVK board.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -246,6 +246,7 @@ properties:
         items:
           - enum:
               - fsl,imx8mn-ddr4-evk       # i.MX8MN DDR4 EVK Board
+              - fsl,imx8mn-evk            # i.MX8MN LPDDR4 EVK Board
           - const: fsl,imx8mn
 
       - description: i.MX8MQ based Boards