(another late reply from me, sorry)

+required:
+  - compatible
+  - reg

This is actually an older IP variant of what can be found in the Intel
LGM SoCs. The dt-bindings are currently being upstreamed for that newer
SoC in [0].

Based on "DOs and DON’Ts for designing and writing Devicetree bindings"
I think some more mandatory properties are needed, even though our
driver currently uses none of them:
- interrupts: as far as I know the IP on the Lantiq SoCs has (at least)
  one interrupt for each DMA channel. That means: 28 interrupts on the
  xRX200 SoCs
- I *assume* (but I have not researched if that's really the case) that
  the Lantiq variant also has at least one clock input and a reset line
- since we don't have a proper DMA driver yet I can't comment what we
  should use for #dma-cells

+examples:
+  - |
+    dma@e104100 {

note to self: it seems that both dma@ and dma-controller@ are used in
existing schemas (the latter having twice as many occurrences though):
$ grep -R dma@ Documentation/devicetree/bindings/dma/* | wc -l
20
$ grep -R dma-controller@ Documentation/devicetree/bindings/dma/* | wc -l
45


Best regards,
Martin


[0] https://patchwork.ozlabs.org/project/devicetree-bindings/patch/0864b9bfa6e2b8b5e7ad9a7a739ca3274f66493c.1610703653.git.mallikarjunax.reddy@linux.intel.com/
[1] https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-bindings.html