drm: drop drmP.h include from drm_plane.c

Just a bit of missing includes and pre declarations.

v2: Compiles now, with drm/drm_util.h extracted.

v3: Rebase

v3: Fix up commit message (Sam Ravnborg)

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180905135711.28370-3-daniel.vetter@ffwll.ch
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 6760e49..0a0834b 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -27,6 +27,8 @@
 #include <linux/ctype.h>
 #include <drm/drm_mode_object.h>
 #include <drm/drm_color_mgmt.h>
+#include <drm/drm_rect.h>
+#include <drm/drm_modeset_lock.h>
 #include <drm/drm_util.h>
 
 struct drm_crtc;