usb: dwc3: Avoid resume_work flush in pm_suspend/pm_resume

dwc3_resume_work is dependent on sm_work which is a freezable task.
When control reaches pm_suspend or pm_resume sm_work is frozen at
that point as part of freeze_processes() api which is called for
system-wide suspend. If there is any pending work on sm_work & we
try to flush when it is frozen we end up in a deadlock as the
suspend/resume thread cannot progress. Avoid flushing this wq in
pm_suspend/resume.

Change-Id: I5eada1c3d11085fcd1b424a1bdb7e0c949f7ef42
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>