dt-bindings: display/xlnx/zynqmp-dpsub: Add audio DMAs

The DP subsystem for ZynqMP supports audio via two channels, and the DP
DMA has dma-engines for those channels. For some reason the DT binding

dt-bindings: display/xlnx/zynqmp-dpsub: Add audio DMAs

The DP subsystem for ZynqMP supports audio via two channels, and the DP
DMA has dma-engines for those channels. For some reason the DT binding
has not specified those channels, even if the picture included in
xlnx,zynqmp-dpsub.yaml shows "2 x aud" DMAs.

This hasn't caused any issues as the drivers have not supported audio,
and has thus gone unnoticed.

To make it possible to add the audio support to the driver, add the two
audio DMAs to the binding. While strictly speaking this is an ABI break,
there should be no regressions caused by this as we're adding new
entries at the end of the dmas list, and, after the audio support has
been added in "arm64: dts: zynqmp: Add DMA for DP audio", the driver
will treat the audio DMAs as optional to also support the old bindings.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241023-xilinx-dp-audio-v4-1-5128881457be@ideasonboard.com

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