drm: make drm/drm_auth.h self contained

Do not require users of include/drm/drm_auth.h to include
other files just to let it build.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
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>
Link: https://patchwork.freedesktop.org/patch/msgid/20190526173535.32701-2-sam@ravnborg.org

include/drm/drm_auth.h

+#ifndef _DRM_AUTH_H_
+#define _DRM_AUTH_H_
+
 /*
  * Internal Header for the Direct Rendering Manager
  *
@@ -25,8 +28,12 @@
  * OTHER DEALINGS IN THE SOFTWARE.
  */
 
-#ifndef _DRM_AUTH_H_
-#define _DRM_AUTH_H_
+#include <linux/idr.h>
+#include <linux/kref.h>
+#include <linux/wait.h>
+
+struct drm_file;
+struct drm_hw_lock;
 
 /*
  * Legacy DRI1 locking data structure. Only here instead of in drm_legacy.h for