vhost-vdpa: uapi to support reporting per vq size

The size of a virtqueue is a per vq configuration.
This commit introduce a new ioctl uAPI to support this flexibility.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Message-Id: <20240202163905.8834-2-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>