ENGR00121385 MX51: Leave MC13892 VUSB Turned on for USB OTG to work

Short-term solution is to leave VUSB always on for USB OTG port
to work. Long-term solution would be for USB driver to enable the
necessary regulators. That will be addressed by a different CR.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>