WF-2881 sysupgrade image uses UBI rootfs, but still relies on
default_do_upgrade. Because of this, config backup is not restored after
sysupgrade. It can be fixed by switching to nand_do_upgrade and
sysupgrade-tar image. default_do_upgrade does not handle sysupgrade-tar
properly, so one should use factory image to upgrade from older version.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>