vfio-ccw: Rework the io_fctl trace

Using __field_struct for the schib is convenient, but it doesn't
appear to let us filter based on any of the schib elements.
Specifying the full schid or any element within it results
in various errors by the parser.  So, expand that out to its
component elements, so we can limit the trace to a single device.

While we are at it, rename this trace to the function name, so we
remember what is being traced instead of an abstract reference to the
function control bit of the SCSW.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20191016142040.14132-5-farman@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>