dt-bindings: arm64: allwinner: h6: Add binding for DMA controller

DMA in H6 is similar to other DMA controller, except it is first which
supports more than 32 request sources and has 16 channels. It also needs
additional clock to be enabled.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>