drm/nouveau: Use private save/restore hooks for CRTCs

I want to remove the core ones since with atomic drivers system
suspend/resume is solved much differently. And there's only 2 drivers
(gma500 besides nouveau) really using them.

v2: Fixup bugs Ilia spotted.

Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449245618-1127-1-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/nouveau/nouveau_crtc.h

@@ -73,6 +73,9 @@ struct nouveau_crtc {
 	int (*set_dither)(struct nouveau_crtc *crtc, bool update);
 	int (*set_scale)(struct nouveau_crtc *crtc, bool update);
 	int (*set_color_vibrance)(struct nouveau_crtc *crtc, bool update);
+
+	void (*save)(struct drm_crtc *crtc);
+	void (*restore)(struct drm_crtc *crtc);
 };
 
 static inline struct nouveau_crtc *nouveau_crtc(struct drm_crtc *crtc)