usb: dwc3: gadget: Implement setting of SSP rate

Implement gadget ops udc_set_ssp_rate(). This allows the gadget/core
driver to select SSP signaling rate and number of lanes to for DWC_usb32
controller.

Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/8998b65fddfa02cab57bfc6aa35e9f101b252068.1611106162.git.Thinh.Nguyen@synopsys.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>