hw/s390x: Remove the "ri_allowed" switch

hw/s390x: Remove the "ri_allowed" switch

Only s390-ccw-virtio-2.6 and older used to set this switch to "off",
for newer machine types it is always enabled. Since we removed the
old machine types now, we can also remove the switch in the code and
assume that it is always enabled now.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Message-ID: <20250103144232.520383-5-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>