This patch achieves multiple goals:
- Align WR841 boardnames with image names
- Fix wrong name replace in sysupgrade
- Support sysupgrade of WR841 v12

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Tim Niemeyer <tim@tn-x.org>
- Rebased
Signed-off-by: Tim Niemeyer <tim@tn-x.org>