dt-bindings: serial: mtk-uart: add support for MT8516

Add binding documentation of mtk-uart for MT8516 SoC.
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>

Documentation/devicetree/bindings/serial/mtk-uart.txt

@@ -17,6 +17,7 @@ Required properties:
   * "mediatek,mt8127-uart" for MT8127 compatible UARTS
   * "mediatek,mt8135-uart" for MT8135 compatible UARTS
   * "mediatek,mt8173-uart" for MT8173 compatible UARTS
+  * "mediatek,mt8516-uart" for MT8516 compatible UARTS
   * "mediatek,mt6577-uart" for MT6577 and all of the above
 
 - reg: The base address of the UART register bank.