ARM: dts: da850: use new 'dma-channels' property

The '#dma-channels' property was deprecated in favor of one defined by
generic dma-common DT bindings.  Add new property while keeping old one
for backwards compatibility.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220516142857.6419-3-krzysztof.kozlowski@linaro.org

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>