usb: xceiv: patches for v3.7 merge window

nop xceiv got its own header to avoid polluting otg.h. It has also
learned to work as USB2 and USB3 phys so we can use it on USB3
controllers.

Together with those two changes to nop xceiv, we're adding basic
PHY support to dwc3 driver, this is to allow platforms which actually
have a SW-controllable PHY talk to them through dwc3 driver.

We're adding a new phy driver for the OMAP architecture. This driver
is for the PHY found in OMAP4 SoCs, and a new phy driver for the
marvell architecture. An extra phy driver - for Tegra SoCs - is now
moving from arch/arm/mach-tegra* to drivers/usb/phy.

Also here, there's the creation of <linux/usb/phy.h> which should be
used from now on for PHY drivers, even those which don't support
OTG.