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_bufs.c b/drivers/gpu/drm/drm_bufs.c
index 61e1ef9..30372f7 100644
--- a/drivers/gpu/drm/drm_bufs.c
+++ b/drivers/gpu/drm/drm_bufs.c
@@ -36,6 +36,7 @@
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
 #include <linux/log2.h>
+#include <linux/export.h>
 #include <asm/shmparam.h>
 #include "drmP.h"