qemu: format SLIC ACPI table command line
    
    <os>
      <acpi>
        <table type="slic">/path/to/acpi/table/file</table>
      </acpi>
    </os>
    
    will result in:
    
    -acpitable sig=SLIC,file=/path/to/acpi/table/file
    
    This option was introduced by QEMU commit 8a92ea2 in 2009.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1327537