MXC: Add support for ULPI Viewports

The ARC USB OTG Core has support for accessing ULPI tranceivers
through so called ULPI viewports. Export a set of function for use with
the USB OTG framework.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>