usb: dwc3: Stop active transfers before halting the controller

In the DWC3 databook, for a device initiated disconnect or bus reset, the
driver is required to send dependxfer commands for any pending transfers.
In addition, before the controller can move to the halted state, the SW
needs to acknowledge any pending events.  If the controller is not halted
properly, there is a chance the controller will continue accessing stale or
freed TRBs and buffers.

Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Reviewed-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>