vfio/ccw: Create an OPEN FSM Event

vfio/ccw: Create an OPEN FSM Event

Move the process of enabling a subchannel for use by vfio-ccw
into the FSM, such that it can manage the sequence of lifecycle
events for the device.

That is, if the FSM state is NOT_OPER(erational), then do the work
that would enable the subchannel and move the FSM to STANDBY state.
An attempt to perform this event again from any of the other operating
states (IDLE, CP_PROCESSING, CP_PENDING) will convert the device back
to NOT_OPER so the configuration process can be started again.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/20220707135737.720765-9-farman@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>