staging: unisys: Prepare vbus_hdr_info to be public

In order to remove bus_info, we need to migrate vbus_hdr_info into
the public namespace of visor_device.  Because the struct is private,
we use a void * to hide the contents.

As a result, we need to allocate vbus_hdr_info and manage it.

Also work around vbus_valid, as that variable will not be used
in the public namespace.

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>