qemu: Add virtio related options to vsock

Add virtio related options iommu, ats and packed as driver element attributes
to vsock devices. Ex:

 <vsock model='virtio'>
   <cid auto='no' address='3'/>
   <driver iommu='on'/>
 </vsock>

Signed-off-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tests/qemuxml2argvdata/vhost-vsock-ccw-iommu.s390x-latest.args

@@ -0,0 +1,42 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/tmp/lib/domain--1-QEMUGuest1 \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/tmp/lib/domain--1-QEMUGuest1/.local/share \
+XDG_CACHE_HOME=/tmp/lib/domain--1-QEMUGuest1/.cache \
+XDG_CONFIG_HOME=/tmp/lib/domain--1-QEMUGuest1/.config \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-s390x \
+-name guest=QEMUGuest1,debug-threads=on \
+-S \
+-object secret,id=masterKey0,format=raw,\
+file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
+-machine s390-ccw-virtio,accel=tcg,usb=off,dump-guest-core=off,\
+memory-backend=s390.ram \
+-cpu qemu \
+-m 214 \
+-object memory-backend-ram,id=s390.ram,size=224395264 \
+-overcommit mem-lock=off \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-boot strict=on \
+-blockdev '{"driver":"host_device","filename":"/dev/HostVG/QEMUGuest1",\
+"node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \
+-blockdev '{"node-name":"libvirt-1-format","read-only":false,"driver":"raw",\
+"file":"libvirt-1-storage"}' \
+-device virtio-blk-ccw,devno=fe.0.0000,drive=libvirt-1-format,id=virtio-disk0,\
+bootindex=1 \
+-device virtio-balloon-ccw,id=balloon0,devno=fe.0.0001 \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\
+resourcecontrol=deny \
+-device vhost-vsock-ccw,id=vsock0,guest-cid=4,vhostfd=6789,iommu_platform=on,\
+devno=fe.0.0002 \
+-msg timestamp=on