ARM: mv78xx0: un-deprecate Terastation WXL

This board is still being worked on by the Debian-on-Buffalo
project, so let's leave it in the tree for now.

Link: https://github.com/1000001101000/Debian_on_Buffalo


Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Gregory Clement <gregory.clement@bootlin.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>