usb: dwc2: gadget: ignore pm suspend/resume in L2

Nothing to be done in pm suspend/resume when controller is in L2.
Don't disconnect or reset. State is already saved when putting
controller in hibernation and will be restored on USB bus resume.

Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Gregory Herrero <gregory.herrero@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>