pci: uniphier: Add UniPhier PCIe controller driver

Add PCIe driver for UniPhier SoCs. This PCIe controller is based on
Synopsys DesignWare Core IP.

This version doesn't apply common DW functions because supported
controller doesn't have unroll version of iATU.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>