Discussion on the mailing list reveals that this target has active
users. As we are finally able to upgrade this target to kernel 5.4,
add it back to master.
This reverts commit 7d29a55714 ("ath25: drop target") and
immediately moves the relevant files to 5.4, without touching
the content.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
