usb: gadget: f_ipc: Add support of sideband notifier call chain

Due to host is in suspend mode the write operation on usb endpoint
is fail so register sideband signal to notify the GPIO driver with
"EVT_WAKE_UP" event, so GPIO driver will wakeup the host as per
event. due to the sideband signalling mechanism, peripheral is able
to send important message after host is coming out from suspend.

Change-Id: I1196f265464ab13e55c1a69fbeb22a1d85d19dcb
Signed-off-by: Aniket Randive <arandive@codeaurora.org>