dt-bindings: arm: amlogic: add support for the Tronsmart MXIII Plus

Add the binding documentation for the Tronsmart MXIII Plus which is an
Android TV box using the Amlogic S812 (Meson8m2) SoC.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

Documentation/devicetree/bindings/arm/amlogic.txt

@@ -58,6 +58,8 @@ Board compatible values (alphabetically, grouped by SoC):
   - "hardkernel,odroid-c1" (Meson8b)
   - "tronfy,mxq" (Meson8b)
 
+  - "tronsmart,mxiii-plus" (Meson8m2)
+
   - "amlogic,p200" (Meson gxbb)
   - "amlogic,p201" (Meson gxbb)
   - "friendlyarm,nanopi-k2" (Meson gxbb)