dmaengine: shdma: prepare to stop using struct dma_chan::private

Using struct dma_chan::private is deprecated. To update the shdma driver to
stop using it we first have to eliminate internal runtime uses of it. After
that we will also be able to stop using it for channel configuration.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>

include/linux/shdma-base.h

@@ -66,6 +66,7 @@ struct shdma_chan {
 	size_t max_xfer_len;		/* max transfer length */
 	int id;				/* Raw id of this channel */
 	int irq;			/* Channel IRQ */
+	struct shdma_slave *slave;	/* Client data for slave DMA */
 	enum shdma_pm_state pm_state;
 };