usb: gadget: send usb_gadget as an argument in get_config_params

Passing struct usb_gadget * as an extra argument in get_config_params
makes gadget drivers to easily update the U1DevExitLat & U2DevExitLat
values based on the values passed from the device tree. This patch
does the same

Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>