dt-bindings: dma: Add Apple ADMAC

Apple's Audio DMA Controller (ADMAC) is used to fetch and store audio
samples on SoCs from the "Apple Silicon" family.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20220531213615.7822-2-povik+lin@cutebit.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>