Add support for EOI with APIC

New options is added to support EOI (End of Interrupt) exposure for
guests. As it makes sense only when APIC is enabled, I added this into
the <apic> element in <features> because this should be tri-state
option (cannot be handled as standalone feature).

docs/formatdomain.html.in

@@ -1018,6 +1018,13 @@
       <dd>ACPI is useful for power management, for example, with
         KVM guests it is required for graceful shutdown to work.
       </dd>
+      <dt><code>apic</code></dt>
+      <dd>APIC allows the use of programmable IRQ
+      management. <span class="since">Since 0.10.2 (QEMU only)</span>
+      there is an optional attribute <code>eoi</code> with values "on"
+      and "off" which toggles the availability of EOI (End of
+      Interrupt) for the guest.
+      </dd>
       <dt><code>hap</code></dt>
       <dd>Enable use of Hardware Assisted Paging if available in
         the hardware.

docs/schemas/domaincommon.rng

@@ -2910,7 +2910,14 @@
           </optional>
           <optional>
             <element name="apic">
-              <empty/>
+              <optional>
+                <attribute name="eoi">
+                  <choice>
+                    <value>on</value>
+                    <value>off</value>
+                  </choice>
+                </attribute>
+              </optional>
             </element>
           </optional>
           <optional>