MIPS: Loongson64: Define PCI_IOBASE

PCI_IOBASE is used to create VM maps for PCI I/O ports, it is
required by generic PCI drivers to make memory mapped I/O range
work.

To deal with legacy drivers that have fixed I/O ports range we
reserved 0x10000 in PCI_IOBASE, should be enough for i8259 i8042
stuff.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>