drm/nouveau/nvif: split out nvsw interface definitons

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv04_fence.c

@@ -26,6 +26,8 @@
 #include "nouveau_dma.h"
 #include "nouveau_fence.h"
 
+#include <nvif/if0004.h>
+
 struct nv04_fence_chan {
 	struct nouveau_fence_chan base;
 };