usb: dwc3: gadget: Update dwc->link_state on connect interrupt

Currently dwc3->link_state is being updated from reset, disconnect,
wakeup and suspend interrupt context. It is being seen that on reset,
link state is still DWC3_LINK_STATE_U3 which causing some of function
driver's control/interrupt transfer to fail as it tries to perform
remote wakeup functionality and keep retrying it. With that host is
trying to re-enumerate device. Fix this issue by updating link state
on receiving connect interrupt where host is already successfully
perform speed detection and device side usb is moved into operational
DWC3_LINK_STATE_U0 state.

Change-Id: I3052eb8bd4e629587ad967d7243b87e7cdb2587b
Signed-off-by: Mayank Rana <mrana@codeaurora.org>