usb: gadget: Fix issue in queuing notification req upon function suspend

Selective suspend of device with remote-wakeup enabled by host
could race with device driver queuing a notification request on
interrupt endpoint. Driver calling usb_func_ep_queue() directly
and issues function wakeup command to controller and returns success to
the function driver. As a result notification request is not queued to
endpoint but returns with success and notify_req_queued remains true.
If function driver tries to queue any request further this results into
request drop as request is already queued.

Hence return -EAGAIN in usb_func_ep_queue to queue the notification request
upon function resume. Also initiate remote wakeup immediately after suspend
if notification request already queued to controller.

Change-Id: I7ac9231c44e8126a043886f5d6cedde491ff818d
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>