dt-bindings: arm: fsl: add IMX8MN DDR3L eval board

This eval board features an IMX8MN UltraLite and has DDR3L RAM. The
product part number is 8MNANOD3L-EVK.
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Heiko Thiery <heiko.thiery@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -876,6 +876,7 @@ properties:
               - beacon,imx8mn-beacon-kit  # i.MX8MN Beacon Development Kit
               - bsh,imx8mn-bsh-smm-s2     # i.MX8MN BSH SystemMaster S2
               - bsh,imx8mn-bsh-smm-s2pro  # i.MX8MN BSH SystemMaster S2 PRO
+              - fsl,imx8mn-ddr3l-evk      # i.MX8MN DDR3L EVK Board
               - fsl,imx8mn-ddr4-evk       # i.MX8MN DDR4 EVK Board
               - fsl,imx8mn-evk            # i.MX8MN LPDDR4 EVK Board
               - gw,imx8mn-gw7902          # i.MX8MM Gateworks Board