drm: make drm_framebuffer.h self contained

Add forward declaration and pull in include
file to make drm_framebuffer.h self contained.

While add it order include files alphabetically.

The use of TASK_COMM_LEN is the reason for including sched.h.
I could not see any good way to avoid this dependency,
and users of drm_framebuffer.comm already use
TASK_COMM_LEN to check for length etc.

v2:
- Added forward declaration of drm_gem_object (Noralf)
- Added ack from Noralf
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108192939.15255-4-sam@ravnborg.org

include/drm/drm_framebuffer.h

@@ -23,13 +23,17 @@
 #ifndef __DRM_FRAMEBUFFER_H__
 #define __DRM_FRAMEBUFFER_H__
 
-#include <linux/list.h>
 #include <linux/ctype.h>
+#include <linux/list.h>
+#include <linux/sched.h>
+
 #include <drm/drm_mode_object.h>
 
-struct drm_framebuffer;
-struct drm_file;
+struct drm_clip_rect;
 struct drm_device;
+struct drm_file;
+struct drm_framebuffer;
+struct drm_gem_object;
 
 /**
  * struct drm_framebuffer_funcs - framebuffer hooks