usb gadget serial: use composite gadget framework

This switches the serial gadget over to using the new "function"
versions of the serial port interfacing code.  The remaining code
in the main source file is quite small...
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/u_serial.h

@@ -41,11 +41,6 @@ struct gserial {
 
 	/* REVISIT avoid this CDC-ACM support harder ... */
 	struct usb_cdc_line_coding port_line_coding;	/* 9600-8-N-1 etc */
-
-	/* FIXME remove these when we switch to acm_bind_config... */
-	struct usb_ep			*notify;
-	struct usb_endpoint_descriptor	*notify_desc;
-	u16				port_handshake_bits;
 };
 
 /* port setup/teardown is handled by gadget driver */