dmaengine: dw: enable and disable controller when needed

Enable controller automatically whenever first user requires for a channel and
disable it when the last user gone.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
diff --git a/drivers/dma/dw/regs.h b/drivers/dma/dw/regs.h
index e8f92b2..848e232 100644
--- a/drivers/dma/dw/regs.h
+++ b/drivers/dma/dw/regs.h
@@ -281,6 +281,7 @@
 	/* channels */
 	struct dw_dma_chan	*chan;
 	u8			all_chan_mask;
+	u8			in_use;
 
 	/* hardware configuration */
 	unsigned char		nr_masters;