usb: otg: Rename otg_transceiver to usb_phy

This is the first step in separating USB transceivers from
USB OTG utilities.

Includes fixes to IMX code from Sascha Hauer.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Acked-by: Li Yang <leoli@freescale.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>