arm64: dts: sprd: 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>
Reviewed-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/20220516142857.6419-4-krzysztof.kozlowski@linaro.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
