drm/nouveau: remove as much direct use of core headers as possible

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
index 6ae0304..4afef92 100644
--- a/drivers/gpu/drm/nouveau/nv50_display.c
+++ b/drivers/gpu/drm/nouveau/nv50_display.c
@@ -28,6 +28,8 @@
 #include <drm/drm_crtc_helper.h>
 #include <drm/drm_dp_helper.h>
 
+#include <nvif/class.h>
+
 #include "nouveau_drm.h"
 #include "nouveau_dma.h"
 #include "nouveau_gem.h"
@@ -37,8 +39,6 @@
 #include "nouveau_fence.h"
 #include "nv50_display.h"
 
-#include <core/class.h>
-
 #define EVO_DMA_NR 9
 
 #define EVO_MASTER  (0x00)