MIPS: malta: add DT bindings for PCI host controller

Add DT binding for GT64120 and MSC01 PCI controllers. Only
GT64120 is enabled by default to support Qemu. The MSC01 node
will be dynamically enabled by Malta board code dependent
on the plugged core card.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>