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.

Signed-off-by: Macpaul Lin <macpaul@gmail.com>
Signed-off-by: Li Jun <jun.li@freescale.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>