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/ati_pcigart.c b/drivers/gpu/drm/ati_pcigart.c
index 1c36492..9afe495 100644
--- a/drivers/gpu/drm/ati_pcigart.c
+++ b/drivers/gpu/drm/ati_pcigart.c
@@ -31,6 +31,7 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/export.h>
 #include "drmP.h"
 
 # define ATI_PCIGART_PAGE_SIZE		4096	/**< PCI GART page size */