dt-bindings: dma: mtk-apdma: add bindings for MT8516 SOC

Add bindings to APDMA for MT8516 SoC. MT8516 is compatible with MT6577.
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201209114736.70625-1-fparent@baylibre.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/dma/mtk-uart-apdma.txt

@@ -4,6 +4,7 @@ Required properties:
 - compatible should contain:
   * "mediatek,mt2712-uart-dma" for MT2712 compatible APDMA
   * "mediatek,mt6577-uart-dma" for MT6577 and all of the above
+  * "mediatek,mt8516-uart-dma", "mediatek,mt6577" for MT8516 SoC
 
 - reg: The base address of the APDMA register bank.