include: usb: add iterable section in ram for usb_cfg_data

Add iterable section in ram for struct usb_cfg_data and
new makro USBD_DEFINE_CFG_DATA which should be used to
define usb_cfg_date structures.

Deprecate makro USBD_CFG_DATA_DEFINE.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>