usb: f_gsi: Configure fixed GSI endpoints and related EP OPs

GSI endpoints are now fixed and need to be requested by name.
As the specific GSI endpoints or ops do not change,
it is not required to be updated on every connect/disconnect
of the cable. This will also fix suspend/disconnect race
conditions.

CRs-Fixed: 946385

Change-Id: I36de64ea95470cb19eb3f084b518618a2fe9f0df
Signed-off-by: Devdutt Patnaik <dpatnaik@codeaurora.org>