PCI: armada: Add driver for Marvell Armada 7K/8K PCIe controller

The Marvell Armada 7K/8K SoCs integrate a PCIe controller from Synopsys.
Add a new driver that provides the small glue needed to use the existing
Designware driver to make it work on Marvell Armada 7K/8K SoCs.

The MSI support will be enabled at a later point.

[bhelgaas: use dev_dbg(), dw_pcie_wait_for_link()]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>