hw/s390x: Restrict "loadparm" property to devices that can be used for booting

hw/s390x: Restrict "loadparm" property to devices that can be used for booting

Commit bb185de423 ("s390x: Add individual loadparm assignment to
CCW device") added a "loadparm" property to all CCW devices. This
was a little bit unfortunate, since this property is only useful
for devices that can be used for booting, but certainly it is not
useful for devices like virtio-gpu or virtio-tablet.

Thus let's restrict the property to CCW devices that we can boot from
(i.e. virtio-block, virtio-net and vfio-ccw devices).

Message-ID: <20241113114741.681096-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Jared Rossi <jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>