ARM: footbridge: mark cats board for removal

There are three remaining footbridge boards, as the CO285 and the HP
personal server got removed already over the years.

Russell still uses his ebsa285, while both Linus and Marc have a NetWinder
that they use for testing. Nobody so far replied that they are using cats,
so it goes on the long list of machines to be removed in early 2023 if
it stays like this.

Cc: Russell King <linux@armlinux.org.uk>
Cc: Linus Walleij <linusw@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>