<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