arm64: dts: Add APM X-Gene PCIe device tree nodes

Add the device tree nodes for APM X-Gene PCIe host controller and PCIe
clock interface.  Since X-Gene SOC supports maximum 5 ports, 5 dts nodes
are added.

Signed-off-by: Tanmay Inamdar <tinamdar@apm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>