dt-bindings: dmaengine: fsl-imx: deprecate '#dma-channels' and '#dma-requests'

The generic properties, used in most of the drivers and defined in
generic dma-common DT bindings, are 'dma-channels' and 'dma-requests'.

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