PCI: visconti: Add Toshiba Visconti PCIe host controller driver

Add support for the PCIe RC controller on Toshiba Visconti ARM SoCs.  This
PCIe controller is based on the Synopsys DesignWare PCIe core.

Link: https://lore.kernel.org/r/20210811083830.784065-3-nobuhiro1.iwamatsu@toshiba.co.jp


Signed-off-by: Yuji Ishikawa <yuji2.ishikawa@toshiba.co.jp>
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>