MLK-11123-1 usb: add usb_otg20_descriptor for OTG 2.0 and above

OTG 2.0 introduces bcdOTG in otg descriptor to identify the OTG and EH
supplement release number with which the OTG device is compliant, this
patch adds structure usb_otg20_descriptor for OTG 2.0 and above. Then
the bcdOTG should be removed for usb_otg_descriptor in gadget drivers.

Signed-off-by: Macpaul Lin <macpaul@gmail.com>
Signed-off-by: Li Jun <jun.li@freescale.com>