staging: unisys: Dissolve visorchannel.h

This header is needed by other drivers and should be in a global namespace.
In addition, functionally it is part of visorbus, so roll the contents
into that header file.

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>