usb: dwc3: Add support to defer suspend after USB LPM

On USB cable disconnect, it is expected to receiv SUSPEND event
followed DISCONNCET event. In both cases, USB is put into LPM
with different power rails turned-off and allowing system suspend
functionality. It is required to defer system suspend till both
events are handled. This change adds support to add configurable
delay for this functionality.

CRs-Fixed: 677740
Change-Id: I0ff3045a3681feb6ddb6b6390e0c1864a17d26c0
Signed-off-by: Mayank Rana <mrana@codeaurora.org>