hw/s390x/css-bridge: switch virtual-css bus to 3-phase-reset

hw/s390x/css-bridge: switch virtual-css bus to 3-phase-reset

Switch the s390x virtual-css bus from using BusClass::reset to the
Resettable interface.

This has no behavioural change, because the BusClass code to support
subclasses that use the legacy BusClass::reset will call that method
in the hold phase of 3-phase reset.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Cédric Le Goater <clg@redhat.com>
Acked-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Tested-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Message-id: 20240119163512.3810301-5-peter.maydell@linaro.org