ppc4xx: Pass PCIe root-complex/endpoint configuration to Linux via the fdt

ppc4xx: Pass PCIe root-complex/endpoint configuration to Linux via the fdt

The PCIe root-complex/endpoint setup as configured via the "pcie_mode"
environment variable will now get passed to the Linux kernel by setting
the device_type property of the PCIe device tree node. For normal root-
complex configuration it will keep its defaults value of "pci" and for
endpoint configuration it will get changed to "pci-endpoint".

Signed-off-by: Stefan Roese <sr@denx.de>