staging: unisys: Move visorbus.h to public namespace

Turn visorbus.h into a public header that all visor* drivers will
include.
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Signed-off-by: NBenjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>