usb: otg: Separate otg members from usb_phy

Introducing struct otg and collecting otg specific members
to it from struct usb_phy. There are no changes to
struct usb_phy at this stage. This also renames
transceiver specific functions, and offers aliases for the
old otg ones.

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>