usb: sandbox: Add gadget callbacks

Add usb_gadget_handle_interrupts(), usb_gadget_register_driver()
and usb_gadget_unregister_driver() to be able to test
binding usb gadget.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/usb/host/usb-sandbox.c b/drivers/usb/host/usb-sandbox.c
index d7cc92a..d1103dc 100644
--- a/drivers/usb/host/usb-sandbox.c
+++ b/drivers/usb/host/usb-sandbox.c
@@ -9,6 +9,13 @@
 #include <log.h>
 #include <usb.h>
 #include <dm/root.h>
+#include <linux/usb/gadget.h>
+
+struct sandbox_udc {
+	struct usb_gadget gadget;
+};
+
+struct sandbox_udc *this_controller;
 
 struct sandbox_usb_ctrl {
 	int rootdev;
@@ -117,6 +124,27 @@
 	return ret;
 }
 
+int usb_gadget_handle_interrupts(int index)
+{
+	return 0;
+}
+
+int usb_gadget_register_driver(struct usb_gadget_driver *driver)
+{
+	struct sandbox_udc *dev = this_controller;
+
+	return driver->bind(&dev->gadget);
+}
+
+int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
+{
+	struct sandbox_udc *dev = this_controller;
+
+	driver->unbind(&dev->gadget);
+
+	return 0;
+}
+
 static int sandbox_alloc_device(struct udevice *dev, struct usb_device *udev)
 {
 	struct sandbox_usb_ctrl *ctrl = dev_get_priv(dev);