[ARM] Orion: distinguish between physical and virtual addresses

Hack up the Orion port to distinguish between virtual and physical
addresses of register windows.  This will allow moving virtual
mappings higher up in the address space, to free up more kernel
virtual address space.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>