iop13xx: use more regular PCI I/O space handling

iop13xx confuses I/O port numbers with physical addresses, which breaks
legacy ISA I/O access behind PCI bridges and makes it unnecessarily hard
to unify the inb/outb accessors with other platforms. This removes the
special-casing and just puts all I/O ports into a single 128KB virtually
mapped I/O port range starting at port zero.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>