PCI: hisi: Add HiSilicon STB SoC PCIe controller driver

Add a HiSilicon STB SoC PCIe controller driver.  This controller is based
on the DesignWare PCIe core.

Signed-off-by: Jianguo Sun <sunjianguo1@huawei.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>