dm: usb: Add a uclass for USB controllers

Add a uclass that can represent a USB controller. For now we do not create
devices for things attached to the controller. This will be added later.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/usb/host/Makefile b/drivers/usb/host/Makefile
index eb6f34b..9419295 100644
--- a/drivers/usb/host/Makefile
+++ b/drivers/usb/host/Makefile
@@ -5,6 +5,10 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+ifdef CONFIG_DM_USB
+obj-$(CONFIG_CMD_USB) += usb-uclass.o
+endif
+
 # ohci
 obj-$(CONFIG_USB_OHCI_NEW) += ohci-hcd.o
 obj-$(CONFIG_USB_ATMEL) += ohci-at91.o