usb: otg: Remove OTG specific members from usb_phy

All the drivers are now converted to use struct usb_otg, so
removing the OTG specific members from struct usb_phy.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>