Xext: _X_EXPORT DPMSSet and DPMSSupported

These are needed by drivers, and it's better to export them from here
rather than redefining them in hw/xfree86 and exporting them from there.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

Xext/dpmsproc.h

@@ -9,7 +9,7 @@
 
 #include "dixstruct.h"
 
-int DPMSSet(ClientPtr client, int level);
+int _X_EXPORT DPMSSet(ClientPtr client, int level);
-Bool DPMSSupported(void);
+Bool _X_EXPORT DPMSSupported(void);
 
 #endif