dt-bindings: dma: arm,pl330: Add missing 'iommus' property

The pl330 can be behind an IOMMU which is the case for Arm Juno board.
Add the 'iommus' property allowing for 1 IOMMU entry per channel for
writes and 1 IOMMU entry for reads.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220801210237.1501488-1-robh@kernel.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>