Alloc sprite memory in devices' devPrivates, allow undisplaying cursors.

Improve memory usage by allocating the sprite's memory only to devices that
actually have a sprite and provide means to remove a device's cursor from the
screen (more hotplugging, yay!).
This commit breaks ScreenRec's ABI.

include/dix.h

@@ -424,6 +424,10 @@ extern int DeliverDeviceEvents(
 extern void DefineInitialRootWindow(
     WindowPtr /* win */);
 
+extern void SetupSprite(
+    DeviceIntPtr /* pDev */,
+    ScreenPtr    /* pScreen */);
+
 extern void InitializeSprite(
     DeviceIntPtr /* pDev */,
     WindowPtr    /* pWin */);

include/input.h

@@ -190,6 +190,8 @@ extern int InitAndStartDevices(void);
 
 extern void CloseDownDevices(void);
 
+extern void UndisplayDevices(void);
+
 extern int RemoveDevice(
     DeviceIntPtr /*dev*/);
 

include/scrnintstr.h

@@ -431,6 +431,18 @@ typedef    void (* MarkUnrealizedWindowProcPtr)(
 	WindowPtr /*pWin*/,
 	Bool /*fromConfigure*/);
 
+typedef    void (* UndisplayCursorProcPtr)(
+        DeviceIntPtr /* pDev */,
+        ScreenPtr    /* pScreen */);
+
+typedef    Bool (* DeviceCursorInitializeProcPtr)(
+        DeviceIntPtr /* pDev */,
+        ScreenPtr    /* pScreen */);
+
+typedef    void (* DeviceCursorCleanupProcPtr)(
+        DeviceIntPtr /* pDev */,
+        ScreenPtr    /* pScreen */);
+
 typedef struct _Screen {
     int			myNum;	/* index of this instance in Screens[] */
     ATOM		id;
@@ -587,6 +599,10 @@ typedef struct _Screen {
     ChangeBorderWidthProcPtr	ChangeBorderWidth;
     MarkUnrealizedWindowProcPtr	MarkUnrealizedWindow;
 
+    /* Device cursor procedures */
+    UndisplayCursorProcPtr        UndisplayCursor;
+    DeviceCursorInitializeProcPtr DeviceCursorInitialize;
+    DeviceCursorCleanupProcPtr    DeviceCursorCleanup;
 } ScreenRec;
 
 typedef struct _ScreenInfo {