usb: gadget: ci13xxx: Do not pullup D+ by default on bootup

Driver is enabling softconnect on probe resulting in starting device
controller and pulling up D+ as soon as VBUS is HIGH.
This can cause problems with drivers which registers with UDC during
initialization but are ready for enumeration only after user enables
it later. Disable it and let composite driver explicitly enable it.

Change-Id: I0868a17cf282613e375301c914f1ad536c9e94d2
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>