arm64: allwinner: a64: Add device node for DMA controller

The A64 SoC has a DMA controller that supports 8 DMA channels
to and from various peripherals. The last used DRQ port is 27.

Add a device node for it.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>