usb: dwc2: Add dwc2_core_reset()

dwc2_core_reset() was previously renamed to
dwc2_core_reset_and_dr_force_mode(). Now add back dwc2_core_reset() which
performs only a basic core reset without forcing the mode.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>