dt-bindings: arm: Add i.MX8M Mini Gateworks GW7904 board

Add DT compatible string for i.MX8M Mini based Gateworks GW7904 board.
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -818,6 +818,7 @@ properties:
               - emtrion,emcon-mx8mm-avari # emCON-MX8MM SoM on Avari Base
               - fsl,imx8mm-ddr4-evk       # i.MX8MM DDR4 EVK Board
               - fsl,imx8mm-evk            # i.MX8MM EVK Board
+              - gateworks,imx8mm-gw7904
               - gw,imx8mm-gw71xx-0x       # i.MX8MM Gateworks Development Kit
               - gw,imx8mm-gw72xx-0x       # i.MX8MM Gateworks Development Kit
               - gw,imx8mm-gw73xx-0x       # i.MX8MM Gateworks Development Kit