drivers: usb: Add generic XHCI

Add support for the generic XHCI driver that contains no SoC
specific code. It can be used on platforms that simply work out
of the box, like on emulated platforms.

TEST: Booted on QEMU sbsa machine using the generic xhci driver.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Marek Vasut <marex@denx.de>
diff --git a/drivers/usb/host/Makefile b/drivers/usb/host/Makefile
index 8dad36f..9e88019 100644
--- a/drivers/usb/host/Makefile
+++ b/drivers/usb/host/Makefile
@@ -50,6 +50,7 @@
 obj-$(CONFIG_USB_XHCI_FSL) += xhci-fsl.o
 obj-$(CONFIG_USB_XHCI_MTK) += xhci-mtk.o
 obj-$(CONFIG_USB_XHCI_MVEBU) += xhci-mvebu.o
+obj-$(CONFIG_USB_XHCI_GENERIC) += xhci-generic.o
 obj-$(CONFIG_USB_XHCI_OMAP) += xhci-omap.o
 obj-$(CONFIG_USB_XHCI_PCI) += xhci-pci.o
 obj-$(CONFIG_USB_XHCI_RCAR) += xhci-rcar.o