MIPS: pci: parse memory ranges from devicetree

Implement pci_load_of_ranges on MIPS. Due to lack of test hardware only 32bit
bus width is supported. This function is based on pci_process_bridge_OF_ranges
from powerpc.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3729/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>