MIPS: Cobalt: Fix theoretical port aliasing issue

Because the VIA SuperIO chip only decodes 24 bits of address space but port
address space currently being configured as 32MB there is the theoretical
possibility of aliases within the I/O port address range.

The complicated solution is to reserve all address range that potencially
could cause such aliases.  But with the PCI spec limiting port allocations
for devices to a maximum of 256 bytes 16MB of port address space already is
way more than one would ever expect to be used so we just reduce the port
space to 16MB.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
To: Yoichi Yuasa <yuasa@linux-mips.org>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: linux-mips@linux-mips.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Patchwork: http://patchwork.linux-mips.org/patch/995/