usb: dwc3: Use pwr_event_irq to wakeup if there is no ss_phy_irq

On platforms where there is no support for ss_phy_irq,
pwr_event_irq is used for wakeup events from SS PHY. Add
the proper programming to enable the Superspeed wakeup events
and do not suspend SS PHY to get these wakeup events.

Change-Id: I812fb13f6b59cfab07532d6e42baa9fe46568c03
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>