Add a new XI2Mask struct and a few helper functions.

The current XI2 mask handling is handy for copying (fixed size arrays) but a
pain to deal with otherwise. Add a struct for XI2 masks and the required
accessors.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>

include/inputstr.h

@@ -622,4 +622,10 @@ static inline WindowPtr DeepestSpriteWin(SpritePtr sprite)
     return sprite->spriteTrace[sprite->spriteTraceGood - 1];
 }
 
+struct _XI2Mask {
+    unsigned char **masks;      /* event mask in masks[deviceid][event type byte] */
+    size_t nmasks;              /* number of masks */
+    size_t mask_size;           /* size of each mask in bytes */
+};
+
 #endif /* INPUTSTRUCT_H */