staging: unisys: Move visorbus.h to public namespace

Turn visorbus.h into a public header that all visor* drivers will
include.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>