drm: Allow drivers to modify plane_state in prepare_fb/cleanup_fb

The drivers have to modify the atomic plane state during the prepare_fb
callback so they track allocations, reservations and dependencies for
this atomic operation involving this fb. In particular, how else do we
set the plane->fence from the framebuffer!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20160818180017.20508-1-chris@chris-wilson.co.uk

drivers/gpu/drm/msm/mdp/mdp4/mdp4_plane.c

@@ -99,7 +99,7 @@ static const struct drm_plane_funcs mdp4_plane_funcs = {
 };
 
 static int mdp4_plane_prepare_fb(struct drm_plane *plane,
-		const struct drm_plane_state *new_state)
+				 struct drm_plane_state *new_state)
 {
 	struct mdp4_plane *mdp4_plane = to_mdp4_plane(plane);
 	struct mdp4_kms *mdp4_kms = get_kms(plane);
@@ -113,7 +113,7 @@ static int mdp4_plane_prepare_fb(struct drm_plane *plane,
 }
 
 static void mdp4_plane_cleanup_fb(struct drm_plane *plane,
-		const struct drm_plane_state *old_state)
+				  struct drm_plane_state *old_state)
 {
 	struct mdp4_plane *mdp4_plane = to_mdp4_plane(plane);
 	struct mdp4_kms *mdp4_kms = get_kms(plane);