modesetting: Include dix-config.h from dumb_bo.c

Fixes mmap failures with 32-bit builds.

Signed-off-by: Michel Dänzer <michel@daenzer.net>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

hw/xfree86/drivers/modesetting/dumb_bo.c

@@ -25,6 +25,10 @@
  *
  */
 
+#ifdef HAVE_DIX_CONFIG_H
+#include "dix-config.h"
+#endif
+
 #include "dumb_bo.h"
 
 #include <errno.h>