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

This reverts commit 74cc257a.

Instead, enable the SUSPEND event interrupt on enable_irq as part
of gadget start to be inline with USB specification.

Change-Id: I4c2d6e48a2276b480e112ee203a18a6865f15408
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>