docs: Docs and rng schemas for io_uring

Signed-off-by: NHan Han <hhan@redhat.com>
Reviewed-by: NPeter Krempa <pkrempa@redhat.com>

docs/formatdomain.html.in

@@ -3774,7 +3774,8 @@
           <li>
             The optional <code>io</code> attribute controls specific
             policies on I/O; qemu guests support "threads" and
-            "native". <span class="since">Since 0.8.8</span>
+            "native" <span class="since">Since 0.8.8</span>, io_uring
+            <span class="since">Since 6.3.0 (QEMU 5.0)</span>.
           </li>
           <li>
             The optional <code>ioeventfd</code> attribute allows users to

docs/schemas/domaincommon.rng

@@ -2278,6 +2278,7 @@
       <choice>
         <value>threads</value>
         <value>native</value>
+        <value>io_uring</value>
       </choice>
     </attribute>
   </define>