gpu: add module.h to drivers/gpu files as required.

So that we don't get build failures once the implicit module.h
presence is removed.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/drivers/gpu/drm/mga/mga_drv.c b/drivers/gpu/drm/mga/mga_drv.c
index 42d3187..33daa29 100644
--- a/drivers/gpu/drm/mga/mga_drv.c
+++ b/drivers/gpu/drm/mga/mga_drv.c
@@ -29,6 +29,8 @@
  *    Gareth Hughes <gareth@valinux.com>
  */
 
+#include <linux/module.h>
+
 #include "drmP.h"
 #include "drm.h"
 #include "mga_drm.h"