usb: pci: Add XHCI driver for PCI

Add a driver which locates the available XHCI controllers on the PCI bus
and makes them available.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/usb/host/Makefile b/drivers/usb/host/Makefile
index c11b551..66d6e9a 100644
--- a/drivers/usb/host/Makefile
+++ b/drivers/usb/host/Makefile
@@ -47,6 +47,7 @@
 obj-$(CONFIG_USB_XHCI_KEYSTONE) += xhci-keystone.o
 obj-$(CONFIG_USB_XHCI_EXYNOS) += xhci-exynos5.o
 obj-$(CONFIG_USB_XHCI_OMAP) += xhci-omap.o
+obj-$(CONFIG_USB_XHCI_PCI) += xhci-pci.o
 
 # designware
 obj-$(CONFIG_USB_DWC2) += dwc2.o