xorg/st: fixup builds against later dpms headers.

(cherry picked from master, commit e9d6ab72be)

src/gallium/state_trackers/xorg/xorg_crtc.c

@@ -42,8 +42,12 @@
 #include "xorg_tracker.h"
 #include "xf86Modes.h"
 
+#ifdef HAVE_XEXTPROTO_71
+#include <X11/extensions/dpmsconst.h>
+#else
 #define DPMS_SERVER
 #include <X11/extensions/dpms.h>
+#endif
 
 #include "pipe/p_inlines.h"
 #include "util/u_rect.h"

src/gallium/state_trackers/xorg/xorg_output.c

@@ -42,8 +42,12 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 
+#ifdef HAVE_XEXTPROTO_71
+#include <X11/extensions/dpmsconst.h>
+#else
 #define DPMS_SERVER
 #include <X11/extensions/dpms.h>
+#endif
 
 #include "X11/Xatom.h"