usb: dwc3: gadget: Enable SUSPEND event after CONNECT DONE

Spurious suspend event may arrive before CONNECT DONE, which
may unnecessarily notify to the charger to reduce current
draw to 2mA, only to revert back to 100mA on the subsequent
reset & connection. Instead, only enable the SUSPEND event
interrupt after the initial CONNECT DONE event is handled.

Change-Id: I41e2ff5d9b693757e06059c98fbe8b3a3878abdd
Signed-off-by: Jack Pham <jackp@codeaurora.org>