Add DT bindings for PCIe controller implemented in UniPhier SoCs when
configured in Root Complex (host) mode. This controller is based on
the DesignWare PCIe core.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>