WPS update optimizations:
*) always initialize restore with true, and make the get_action timeout 1 tick if restore is true (which only happens at initially showing the wps), which makes the wps show up way faster (nearly instantly)
*) reduce the number of full updates by removing update_track (full updates are initiated by the event now), rename partial_update to update.
Now, full updates should really happen only on (re-)entering the wps or track change now.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@20661 a1c6a512-1295-4272-9138-f99709370657