arm: imx: Start using struct usb_otg

Use struct usb_otg members with OTG specific functions instead
of usb_phy members.

Includes fixes from Sascha Hauer.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Tested-by: Philippe Rétornaz <philippe.retornaz@epfl.ch>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>