staging: unisys: Convert the device attributes to visor_device

Convert the device attribute files to properly use visor_device.
This removes a whole bunch of checks and assumptions and simplifies
the code.  Everything is straightforward.

No testing down as I can't mimic channel info correctl.

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>