dt-bindings: ARM: tegra: Document Pegatron Chagall

Document Pegatron Chagall, which is Tegra30-based tablet device.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/arm/tegra.yaml

@@ -89,6 +89,9 @@ properties:
       - items:
           - const: ouya,ouya
           - const: nvidia,tegra30
+      - items:
+          - const: pegatron,chagall
+          - const: nvidia,tegra30
       - items:
           - enum:
               - asus,tf701t