drm_modeset_ctl_t fixes.

s/u64/drm_u64_t/ to allow userspace code using drm.h to compile.

Move 64 bit arg member to the beginning to avoid alignment issues with 32
bit userspace on 64 bit kernels.

shared-core/drm.h

@@ -598,8 +598,8 @@ typedef enum {
  * \sa drmModesetCtl().
  */
 typedef struct drm_modeset_ctl {
+	drm_u64_t arg;
 	drm_modeset_ctl_cmd_t cmd;
-	u64 arg;
 } drm_modeset_ctl_t;
 
 /**