usb:gadget:composite: Support for composite at gadget.h

Add device data pointer to the USB gadget's device struct.
Wrapper for extracting usb_gadget from Linux's usb device

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Vasut <marex@denx.de>

include/linux/usb/gadget.h

@@ -411,6 +411,7 @@ struct usb_gadget_ops {
 
 struct device {
 	void		*driver_data;	/* data private to the driver */
+	void            *device_data;   /* data private to the device */
 };
 
 /**
@@ -481,6 +482,11 @@ static inline void *get_gadget_data(struct usb_gadget *gadget)
 	return gadget->dev.driver_data;
 }
 
+static inline struct usb_gadget *dev_to_usb_gadget(struct device *dev)
+{
+	return container_of(dev, struct usb_gadget, dev);
+}
+
 /* iterates the non-control endpoints; 'tmp' is a struct usb_ep pointer */
 #define gadget_for_each_ep(tmp, gadget) \
 	list_for_each_entry(tmp, &(gadget)->ep_list, ep_list)