usb: gadget: dummy_hcd: convert to new-style udc-probe

bind() and pull is moved to udc core, call callbacks are verified by the
upper layer.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>