PCI: amlogic: Add the Amlogic Meson PCIe controller driver

The Amlogic Meson PCIe host controller is based on the Synopsys DesignWare
PCI core. This patch adds the driver support for Meson PCIe controller.

Link: https://lore.kernel.org/linux-pci/20181218224708.GB22610@google.com/
Signed-off-by: Yue Wang <yue.wang@amlogic.com>
Signed-off-by: Hanjie Lin <hanjie.lin@amlogic.com>
[lorenzo.pieralisi@arm.com: updated coding/comment style]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>