* Allows waiting until all spans are "assigned" or "unassigned"
* Current implementation use a polling loop with sleep
* Future implementation may block on sysfs attribute
  (like waitfor_xpds is blocking on sysfs Astribanks attribute)

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Acked-by: Russ Meyerriecks <rmeyerriecks@digium.com>