MIPS: Loongson64: Process ISA Node in DeviceTree

Previously, we're hardcoding reserved ISA I/O Space in, now
we're processing it I/O via DeviceTree directly.
The ranges property if ISA node is used to determine the size and address
of reserved I/O space.

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