usb: gadget: udc: renesas_usb3: should call pm_runtime_enable() before add udc
This patch fixes an issue that this driver causes panic if a gadget
driver is already loaded because usb_add_gadget_udc() might call
renesas_usb3_start() via .udc_start, and then pm_runtime_get_sync()
in renesas_usb3_start() doesn't work correctly.
Note that the usb3_to_dev() macro should not be called at this timing
because the macro uses the gadget structure.