dwc3: gadget: Add handling of bus resume and L1 resume functionality

Dwc3 controller raises wakeup interrupt when there is USB bus resume
or L1 resume initiated by connected host. This change checks link_state
to confirm that previous state was U3 (USB bus or L1 suspend) and resume
USB bus if previously it was suspended.

Change-Id: Ic71aecc493b130e2ea16fc3c70b826f588fe10c8
Signed-off-by: Mayank Rana <mrana@codeaurora.org>