scsi: Add NO_DMA dummies for SCSI DMA mapping API

Add dummies for scsi_dma_{,un}map(), to allow compile-testing if
NO_DMA=y.

This prevents the following from showing up later:

    ERROR: "scsi_dma_unmap" [drivers/firewire/firewire-sbp2.ko] undefined!
    ERROR: "scsi_dma_map" [drivers/firewire/firewire-sbp2.ko] undefined!
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

include/scsi/scsi_cmnd.h

@@ -174,8 +174,13 @@ extern void scsi_kunmap_atomic_sg(void *virt);
 
 extern int scsi_init_io(struct scsi_cmnd *cmd);
 
+#ifdef CONFIG_SCSI_DMA
 extern int scsi_dma_map(struct scsi_cmnd *cmd);
 extern void scsi_dma_unmap(struct scsi_cmnd *cmd);
+#else /* !CONFIG_SCSI_DMA */
+static inline int scsi_dma_map(struct scsi_cmnd *cmd) { return -ENOSYS; }
+static inline void scsi_dma_unmap(struct scsi_cmnd *cmd) { }
+#endif /* !CONFIG_SCSI_DMA */
 
 static inline unsigned scsi_sg_count(struct scsi_cmnd *cmd)
 {