usb: dwc2: gadget: rework suspend/resume code to correctly restore gadget state

Suspend/resume code assumed that the gadget was always started and
enabled to connect to usb bus. This means that the actual state of the
gadget (started/stopped or connected/disconnected) was not correctly
preserved on suspend/resume cycle. This patch fixes this issue.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>