drm/exynos: wait all planes updates to finish

Add infrastructure to wait for all planes updates to finish by using
an atomic_t variable to track how many pending updates we are waiting
plus a wait_queue for the wait part.

It also changes vblank behaviour and keeps it enabled for all types
of updates

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.h b/drivers/gpu/drm/exynos/exynos_drm_crtc.h
index 8bedfde..f87d4ab 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_crtc.h
+++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.h
@@ -25,6 +25,7 @@
 					void *context);
 int exynos_drm_crtc_enable_vblank(struct drm_device *dev, int pipe);
 void exynos_drm_crtc_disable_vblank(struct drm_device *dev, int pipe);
+void exynos_drm_crtc_wait_pending_update(struct exynos_drm_crtc *exynos_crtc);
 void exynos_drm_crtc_finish_update(struct exynos_drm_crtc *exynos_crtc,
 				   struct exynos_drm_plane *exynos_plane);
 void exynos_drm_crtc_complete_scanout(struct drm_framebuffer *fb);