dmaengine: hsu: introduce stubs for the exported functions

This allows UART drivers to register HSU DMA Engine without
being forced to use ifdefs.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/dma/hsu.h

@@ -38,11 +38,21 @@ struct hsu_dma_chip {
 	struct hsu_dma_platform_data	*pdata;
 };
 
+#if IS_ENABLED(CONFIG_HSU_DMA)
 /* Export to the internal users */
 irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip, unsigned short nr);
 
 /* Export to the platform drivers */
 int hsu_dma_probe(struct hsu_dma_chip *chip);
 int hsu_dma_remove(struct hsu_dma_chip *chip);
+#else
+static inline irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip,
+				      unsigned short nr)
+{
+	return IRQ_NONE;
+}
+static inline int hsu_dma_probe(struct hsu_dma_chip *chip) { return -ENODEV; }
+static inline int hsu_dma_remove(struct hsu_dma_chip *chip) { return 0; }
+#endif /* CONFIG_HSU_DMA */
 
 #endif /* _DMA_HSU_H */