If vhost device's IOMMU feature is disabled, IOTLB mempool allocation
is unnecessary.
Reported-by: Peng He <hepeng.0320@bytedance.com>
Signed-off-by: Junjie Wan <wanjunjie@bytedance.com>
Reviewed-by: Zhihong Wang <wangzhihong.wzh@bytedance.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>