dt-bindings: arm: fsl: Document Variscite i.MX6q devicetree

Document the Variscite i.MX6qdl board devicetree binding
already supported:

- variscite,dt6customboard
Signed-off-by: Oliver Graute <oliver.graute@kococonnector.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -121,6 +121,7 @@ properties:
               - fsl,imx6q-sabresd
               - technologic,imx6q-ts4900
               - technologic,imx6q-ts7970
+              - variscite,dt6customboard
           - const: fsl,imx6q
 
       - description: i.MX6QP based Boards