usb: dwc3: gadget: Update link_state based on receiving interrupt

Currently dwc->link_state is being updated by reading DWC3_DSTS
register. DWC3_DSTS register is having delay in updation of LINK
state. Hence instead of relying on this register for U0 and U3
state, update dwc->link_state directly on receiving reset/wakeup
and suspend/disconnect interrupts respectively.

Change-Id: I8640f9566ab21c60fab24a2e5d25ba24545183ff
Signed-off-by: Mayank Rana <mrana@codeaurora.org>
[jackp@codeaurora.org: resolved a trivial context conflict]
Signed-off-by: Jack Pham <jackp@codeaurora.org>