PCI: xgene: Add APM X-Gene PCIe driver

Add the AppliedMicro X-Gene SOC PCIe host controller driver.  The X-Gene
PCIe controller supports up to 8 lanes and GEN3 speed.  The X-Gene SOC
supports up to 5 PCIe ports.

[bhelgaas: folded in MAINTAINERS and bindings updates]
Tested-by: Ming Lei <ming.lei@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Signed-off-by: Tanmay Inamdar <tinamdar@apm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Liviu Dudau <Liviu.Dudau@arm.com> (driver)
diff --git a/drivers/pci/host/Kconfig b/drivers/pci/host/Kconfig
index 8922c37..d55de1b 100644
--- a/drivers/pci/host/Kconfig
+++ b/drivers/pci/host/Kconfig
@@ -63,4 +63,14 @@
 	help
 	  Say Y here if you want PCIe support on SPEAr13XX SoCs.
 
+config PCI_XGENE
+	bool "X-Gene PCIe controller"
+	depends on ARCH_XGENE
+	depends on OF
+	select PCIEPORTBUS
+	help
+	  Say Y here if you want internal PCI support on APM X-Gene SoC.
+	  There are 5 internal PCIe ports available. Each port is GEN3 capable
+	  and have varied lanes from x1 to x8.
+
 endmenu