usb: dwc2: set parameter values in probe function

So the parameters can be used in both host and gadget modes.
Also consolidate param functions in the core.h

Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>