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_dma.c b/drivers/gpu/drm/drm_dma.c
index 252cbd7..cfb4e33 100644
--- a/drivers/gpu/drm/drm_dma.c
+++ b/drivers/gpu/drm/drm_dma.c
@@ -33,6 +33,7 @@
  * OTHER DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/export.h>
 #include "drmP.h"
 
 /**