ARM: dts: imx27: use new 'dma-channels' property

The '#dma-channels' property was deprecated in favor of one defined by
generic dma-common DT bindings.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>