dmaengine: xilinx: Add empty device_config function

Various DMA users call the dmaengine_slave_config() and expect it to
succeed, but that can only succeed if .device_config is implemented.
Add empty device_config function rather than patching all the places
which use dmaengine_slave_config().

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Kedareswara rao Appana <appana.durga.rao@xilinx.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Vinod Koul <vinod.koul@intel.com>

drivers/dma/xilinx/xilinx_dma.c

@@ -1649,6 +1649,17 @@ static void xilinx_dma_issue_pending(struct dma_chan *dchan)
 	spin_unlock_irqrestore(&chan->lock, flags);
 }
 
+/**
+ * xilinx_dma_issue_pending - Configure the DMA channel
+ * @dchan: DMA channel
+ * @config: channel configuration
+ */
+static int xilinx_dma_device_config(struct dma_chan *dchan,
+				    struct dma_slave_config *config)
+{
+	return 0;
+}
+
 /**
  * xilinx_dma_complete_descriptor - Mark the active descriptor as complete
  * @chan : xilinx DMA channel
@@ -3084,6 +3095,7 @@ static int xilinx_dma_probe(struct platform_device *pdev)
 	xdev->common.device_synchronize = xilinx_dma_synchronize;
 	xdev->common.device_tx_status = xilinx_dma_tx_status;
 	xdev->common.device_issue_pending = xilinx_dma_issue_pending;
+	xdev->common.device_config = xilinx_dma_device_config;
 	if (xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
 		dma_cap_set(DMA_CYCLIC, xdev->common.cap_mask);
 		xdev->common.device_prep_slave_sg = xilinx_dma_prep_slave_sg;