usb: dwc3: gadget: Ignore L1 RESUME events

Events may get generated for Link Power Management L1
Suspend and Resume. The suspend case currently ignores
L1 and only proceeds to call the gadget driver suspend
routines if it is for L2/U3 entry. However, the resume
callback doesn't make this distinction, which will
result in the gadget layer resume getting called for
which there had not been a previous suspend.

Change-Id: Ifaa71d2e85bd797154f368e7623bc8ff94b6a727
Signed-off-by: Jack Pham <jackp@codeaurora.org>