The 'pmem' option allows users to specify whether the backend
storage of memory-backend-file is a real persistent memory:

<devices>
  ...
  <memory model='nvdimm' access='shared'>
      <source>
          <path>/dev/dax0.0</path>
          <pmem/>
      </source>
      <target>
          <size unit='MiB'>4094</size>
          <node>0</node>
          <label>
              <size unit='MiB'>2</size>
          </label>
      </target>
  </memory>
  ...
</devices>
Signed-off-by: NLuyao Zhong <luyao.zhong@intel.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>