doc: dt-binding: usb: add otg related properties

Add otg version, srp, hnp and adp support for usb OTG port, then those OTG
features don't have to be decided by usb gadget drivers.

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