dmaengine: provide dummy functions for DMA_ENGINE=n

This lets drivers, optionally using the dmaengine, build with DMA_ENGINE
unselected.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

include/linux/dmaengine.h

@@ -824,6 +824,8 @@ enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie);
 #ifdef CONFIG_DMA_ENGINE
 enum dma_status dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx);
 void dma_issue_pending_all(void);
+struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, void *fn_param);
+void dma_release_channel(struct dma_chan *chan);
 #else
 static inline enum dma_status dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx)
 {
@@ -831,7 +833,14 @@ static inline enum dma_status dma_wait_for_async_tx(struct dma_async_tx_descript
 }
 static inline void dma_issue_pending_all(void)
 {
-	do { } while (0);
+}
+static inline struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask,
+					      dma_filter_fn fn, void *fn_param)
+{
+	return NULL;
+}
+static inline void dma_release_channel(struct dma_chan *chan)
+{
 }
 #endif
 
@@ -842,8 +851,6 @@ void dma_async_device_unregister(struct dma_device *device);
 void dma_run_dependencies(struct dma_async_tx_descriptor *tx);
 struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type);
 #define dma_request_channel(mask, x, y) __dma_request_channel(&(mask), x, y)
-struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, void *fn_param);
-void dma_release_channel(struct dma_chan *chan);
 
 /* --- Helper iov-locking functions --- */