dm: usb: sandbox: Add a driver for sandbox

This driver supports using emulation devices to provide a USB bus within
sandbox.

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 9419295..7658f87 100644
--- a/drivers/usb/host/Makefile
+++ b/drivers/usb/host/Makefile
@@ -7,6 +7,7 @@
 
 ifdef CONFIG_DM_USB
 obj-$(CONFIG_CMD_USB) += usb-uclass.o
+obj-$(CONFIG_SANDBOX) += usb-sandbox.o
 endif
 
 # ohci