usb: gadget: udc: renesas_usb3: fix pm_runtime functions calling

This patch fixes an issue that this driver is possible to access
the registers before pm_runtime_get_sync() if a gadget driver is
installed first. After that, oops happens on R-Car Gen3 environment.
To avoid it, this patch changes the pm_runtime call timing from
probe/remove to udc_start/udc_stop.

Fixes: 746bfe63 ("usb: gadget: renesas_usb3: add support for Renesas USB3.0 peripheral controller")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>