Convert the Arm PL330 DMA controller binding to DT schema.

The '#dma-channels' and '#dma-requests' properties are unused as they are
discoverable and are non-standard (the standard props don't have '#'). So
drop them from the binding.

Cc: Vinod Koul <vkoul@kernel.org>
Cc: dmaengine@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211217170644.3145332-1-robh@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>