ARM: pxa: remove unused board files

The majority of all pxa board files has not been touched in a long time,
and no users have spoken up in favor of keeping them around. This leaves
only support for the platforms that were already converted to DT, as
well as the gumstix and spitz/akita/borzoi machines that work in qemu
and can still be converted to DT later.

Cc: Ales Bardorfer <ales@i-tech.si>
Cc: Ales Snuparek <snuparek@atlas.cz>
Cc: Alex Osborne <ato@meshy.org>
Cc: Alex Osborne <bobofdoom@gmail.com>
Cc: Dirk Opfer <dirk@opfer-online.de>
Cc: Ian Molton <spyro@f2s.com>
Cc: Lennert Buytenhek <kernel@wantstofly.org>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Michael Petchkovsky <mkpetch@internode.on.net>
Cc: Nick Bane <nick@cecomputing.co.uk>
Cc: Paul Parsons <lost.distance@yahoo.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Sergey Lapin <slapin@ossfans.org>
Cc: Tomas Cech <sleep_walker@suse.cz>
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>