usb: dwc2: gadget: Add remote_wakeup_allowed flag

It will be set once corresponding set_feature command comes.

True if device is allowed to wake-up host by remote-wakeup
signalling.

This is preparation for remote wake-up support implementation,
it will not be implemented until gadget stack provide interface
for bringing remote wake-up signalling.

Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Grigor Tovmasyan <tovmasya@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>