usb: dwc3: support continuous runtime PM with dual role

The DRD module calls dwc3_set_mode() on role switches, i.e. when a device is
being plugged in. In order to support continuous runtime power management when
plugging in / unplugging a cable, we need to call pm_runtime_get_sync() in
this path.

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Felipe Balbi <balbi@kernel.org>