vdpa: store x-svq parameter in VhostVDPAState

vdpa: store x-svq parameter in VhostVDPAState

CVQ can be shadowed two ways:
- Device has x-svq=on parameter (current way)
- The device can isolate CVQ in its own vq group

QEMU needs to check for the second condition dynamically, because CVQ
index is not known before the driver ack the features. Since this is
dynamic, the CVQ isolation could vary with different conditions, making
it possible to go from "not isolated group" to "isolated".

Saving the cmdline parameter in an extra field so we never disable CVQ
SVQ in case the device was started with x-svq cmdline.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20221215113144.322011-11-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>