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 <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Sean Paul <[e-mail]>
Cc: David Airlie <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

include/drm/drm_auth.h

···
+#ifndef _DRM_AUTH_H_
+#define _DRM_AUTH_H_
+
 /*
  * Internal Header for the Direct Rendering Manager
  *
···
  * 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