staging: fieldbus: move "offline mode" definition to fieldbus core

anybus-s cards use the "offline mode" property to determine if
process memory should be clear, set, or frozen when the card
is offline.

Move this property to the fieldbus core, so that it can become
part of the future fieldbus config interface.

Signed-off-by: Sven Van Asbroeck <TheSven73@gmail.com>
Link: https://lore.kernel.org/r/20190918183552.28959-3-TheSven73@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>