dt-bindings: tegra: Document Jetson Xavier NX (and devkit)

Add the compatible strings for the Jetson Xavier NX and the
corresponding developer kit.
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/arm/tegra.yaml

@@ -101,3 +101,11 @@ properties:
           - enum:
               - nvidia,p2972-0000
           - const: nvidia,tegra194
+      - description: Jetson Xavier NX
+        items:
+          - const: nvidia,p3668-0000
+          - const: nvidia,tegra194
+      - description: Jetson Xavier NX Developer Kit
+        items:
+          - const: nvidia,p3509-0000+p3668-0000
+          - const: nvidia,tegra194