usb: dwc3: gadget: Allow pullup on/off during LPM

gadget_pullup is currently used as part of dynamic
usb composition switch. If the user try to switch
composition while the core is in low power mode, it
results in unclocked access to usb core registers.
This change insures that the core is not in LPM
during the pullup on/off sequence.

Change-Id: I0b0913674a8fbf5af3d9be40fa749bac251b075a
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>