vfio/ccw: move private initialization to callback

vfio/ccw: move private initialization to callback

There's already a device initialization callback that is used to
initialize the release completion workaround that was introduced
by commit ebb72b765fb49 ("vfio/ccw: Use the new device life cycle
helpers").

Move the other elements of the vfio_ccw_private struct that
require distinct initialization over to that routine.

With that done, the vfio_ccw_alloc_private routine only does a
kzalloc, so fold it inline.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/20221104142007.1314999-4-farman@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>