usb: gadget: Add ep_config call back to usb_gadget_ops

Since some new fields in usb_ep structure been moved to usb_ss_ep.
The CDNS3 gadget driver should replies on this operation to bind the
usb_ss_ep with the endpoint descriptor when function layer uses
usb_ep_autoconfig to add endpoint descriptors to gadget. So that
CDNS3 driver can know the EP information and configure the EP once
the set configuration request is received.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>