gpu: Add export.h as required to drivers/gpu files.

They need this to get all the EXPORT_SYMBOL variants and THIS_MODULE

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ad74fb4..fb8e46b 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -32,6 +32,7 @@
 
 #include <linux/list.h>
 #include <linux/list_sort.h>
+#include <linux/export.h>
 #include "drmP.h"
 #include "drm.h"
 #include "drm_crtc.h"