arm64: dts: mediatek: mt8516: add support for APDMA

Add support the APDMA IP on MT8516. APDMA is a DMA controller
for UARTs.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Link: https://lore.kernel.org/r/20201209114736.70625-2-fparent@baylibre.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>