spi: mxs-spi: move to use generic DMA helper

With the generic DMA device tree helper supported by mxs-dma driver,
client devices only need to call dma_request_slave_channel() for
requesting a DMA channel from dmaengine.

Since mxs is a DT only platform now, along with the changes, the non-DT
case handling in probe function also gets removed.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/include/linux/spi/mxs-spi.h b/include/linux/spi/mxs-spi.h
index 61ae130..4835486 100644
--- a/include/linux/spi/mxs-spi.h
+++ b/include/linux/spi/mxs-spi.h
@@ -24,7 +24,7 @@
 #ifndef __LINUX_SPI_MXS_SPI_H__
 #define __LINUX_SPI_MXS_SPI_H__
 
-#include <linux/fsl/mxs-dma.h>
+#include <linux/dmaengine.h>
 
 #define ssp_is_old(host)	((host)->devid == IMX23_SSP)
 
@@ -137,9 +137,7 @@
 	unsigned int			clk_rate;
 	enum mxs_ssp_id			devid;
 
-	int				dma_channel;
 	struct dma_chan			*dmach;
-	struct mxs_dma_data		dma_data;
 	unsigned int			dma_dir;
 	enum dma_transfer_direction	slave_dirn;
 	u32				ssp_pio_words[SSP_PIO_NUM];