usb: cdns3: gadget: Don't manage pullups

The USB gadget core is supposed to manage pullups
of the controller. Don't manage pullups from within
the controller driver. Otherwise, function drivers
are not able to keep the controller disconnected from
the bus till they are ready. (e.g. g_webcam)

Reviewed-by: Pawel Laszczak <pawell@cadence.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>