staging: unisys: detect controlvm channel on module load

The controlvm channel is not removable from a guest after the guest starts,
so it makes no sense to constantly check for it. Move the channel address
discovery to visorchipset_init(), and remove all of the checks for the channel
address from the rest of the module, as the module will not load if the
channel pointer is not valid.

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