virtio_vdpa: create vqs with the actual size

The size of a virtqueue is a per vq configuration,
this commit allows virtio_vdpa to create
virtqueues with the actual size of a specific
vq size that supported by the backend device.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Message-Id: <20240202163905.8834-9-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>