drm/atomic: Unconditionally call prepare_fb.

Atomic drivers may set properties like rotation on the same fb, which
may require a call to prepare_fb even when framebuffer stays identical.

Instead of handling all the special cases in the core, let the driver
decide when prepare_fb and cleanup_fb are noops.

This is a revert of:

commit fcc60b41
Author: Keith Packard <keithp@keithp.com>
Date:   Sat Jun 4 01:16:22 2016 -0700

    drm: Don't prepare or cleanup unchanging frame buffers [v3]

The original commit mentions that this prevents waiting in i915 on all
previous rendering during cursor updates, but there are better ways to
fix this.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/6d82f9b6-9d16-91d1-d176-4a37b09afc44@linux.intel.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -1671,9 +1671,6 @@ int drm_atomic_helper_prepare_planes(struct drm_device *dev,
 
 		funcs = plane->helper_private;
 
-		if (!drm_atomic_helper_framebuffer_changed(dev, state, plane_state->crtc))
-			continue;
-
 		if (funcs->prepare_fb) {
 			ret = funcs->prepare_fb(plane, plane_state);
 			if (ret)
@@ -1690,9 +1687,6 @@ int drm_atomic_helper_prepare_planes(struct drm_device *dev,
 		if (j >= i)
 			continue;
 
-		if (!drm_atomic_helper_framebuffer_changed(dev, state, plane_state->crtc))
-			continue;
-
 		funcs = plane->helper_private;
 
 		if (funcs->cleanup_fb)
@@ -1959,9 +1953,6 @@ void drm_atomic_helper_cleanup_planes(struct drm_device *dev,
 	for_each_plane_in_state(old_state, plane, plane_state, i) {
 		const struct drm_plane_helper_funcs *funcs;
 
-		if (!drm_atomic_helper_framebuffer_changed(dev, old_state, plane_state->crtc))
-			continue;
-
 		funcs = plane->helper_private;
 
 		if (funcs->cleanup_fb)