Xorg.wrap: activate libdrm based detection for KMS drivers

Xorg.wrap includes code guarded with WITH_LIBDRM for detecting KMS drivers.
Unfortunately it is never activated since code missed to include file
which defines WITH_LIBDRM.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92894
Signed-off-by: Arkadiusz Miśkiewicz <arekm@maven.pl>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

hw/xfree86/xorg-wrapper.c

@@ -24,6 +24,7 @@
  */
 
 #include "dix-config.h"
+#include "xorg-config.h"
 
 #include <errno.h>
 #include <fcntl.h>