Move each screen's x/y origin into ScreenRec.

Many references to the dixScreenOrigins array already had the
corresponding screen pointer handy, which meant they usually looked like
"dixScreenOrigins[pScreen->myNum]". Adding a field to ScreenRec instead
of keeping this information in a parallel array simplifies those
expressions, and eliminates a MAXSCREENS-sized array.

Since dix declared the dixScreenOrigins array, I figure allocating a
screen private for these values is overkill.

Signed-off-by: Jamey Sharp <jamey@minilop.net>
Reviewed-by: Tiago Vignatti <tiago.vignatti@nokia.com>
Tested-by: Tiago Vignatti <tiago.vignatti@nokia.com> (i686 GNU/Linux)

dix/getevents.c

@@ -1210,8 +1210,8 @@ PostSyntheticMotion(DeviceIntPtr pDev,
        will translate from sprite screen to screen 0 upon reentry
        to the DIX layer. */
     if (!noPanoramiXExtension) {
-        x += dixScreenOrigins[0].x - dixScreenOrigins[screen].x;
-        y += dixScreenOrigins[0].y - dixScreenOrigins[screen].y;
+        x += screenInfo.screens[0]->x - screenInfo.screens[screen]->x;
+        y += screenInfo.screens[0]->y - screenInfo.screens[screen]->y;
     }
 #endif