conf: Add support for setting Chassis SMBIOS data fields

conf: Add support for setting Chassis SMBIOS data fields

This type of information defines attributes of a system
chassis, such as SMBIOS Chassis Asset Tag.

access inside VM (for example)
Linux:   /sys/class/dmi/id/chassis_asset_tag.
Windows: (Get-WmiObject Win32_SystemEnclosure).SMBIOSAssetTag
          wirhin Windows PowerShell.

As an example, add the following to the guest XML

    <chassis>
      <entry name='manufacturer'>Dell Inc.</entry>
      <entry name='version'>2.12</entry>
      <entry name='serial'>65X0XF2</entry>
      <entry name='asset'>40000101</entry>
      <entry name='sku'>Type3Sku1</entry>
    </chassis>

Signed-off-by: Zhuang Yanying <ann.zhuangyanying@huawei.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>