dm: usb: tegra: Store the controller type explicitly

At present the tegra driver uses a separate pointer to know which controller
type is in use. This works because only one controller type is used at a
time.

With driver model we want to make the controller state hermetic in the sense
that it is not necessary to look elsewhere to know the controller type. This
will permit a controller to implement the EHCI weak functions without
reference to global data structures.

To achieve this, define an enum for the controller type and store it with
the information on each EHCI controller.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>