dmaengine: sprd: Change channel id to slave id for DMA cell specifier

We will describe the slave id in DMA cell specifier instead of DMA channel
id, thus we should save the slave id from DMA engine translation function,
and remove the channel id validation.

Meanwhile we do not need set default slave id in sprd_dma_alloc_chan_resources(),
remove it.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>