ARM: footbridge: use fixed PCI i/o mapping

Move footbridge PCI to fixed i/o mapping. io.h is still needed for the
!MMU case.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Russell King <linux@arm.linux.org.uk>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>