arm64: dts: mediatek: mt6795: Add support for APDMA and wire up UART DMAs

arm64: dts: mediatek: mt6795: Add support for APDMA and wire up UART DMAs

This SoC has a DMA controller with tx/rx channels for all of the
UART controller IPs: add the apdma node and wire up the DMAs on
all controllers.
When one of the UART controllers is used as a serial console,
the DMA will be automatically ignored.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221027095504.37432-4-angelogioacchino.delregno@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>