usb: otg: twl4030-usb: ignore duplicate events

In some rare cases we may get multiple interrupts that will generate
duplicate events. This is a problem because each VBUS/ID event generates
runtime_pm call in OMAP glue code, causing unbalanced gets or puts
and breaking PM. Also twl4030_usb_linkstat() may break OTG state
machine by overriding back to old state after state has already
progressed from previous event, so we must ignore dupes.
The same goes for initial state obtained in init too.