ARM: ep93xx: remove old board files

These five board files were marked as unused a while ago, and
nobody wanted to keep them around for longer, so remove them
now.

We still have the edb93xx, visision_ep9307 and ts72xx files,
which can hopefully be converted to device tree in the future.

Cc: Lennert Buytenhek <kernel@wantstofly.org>
Cc: Hubert Feurstein <hubert.feurstein@contec.at>
Acked-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>