schemas: domcaps: Make more elements optional

Upcoming changes will make outputting these subelements optional.

While we are here drop the useless interleave: since this is an output
only format the elements are always in the same order
Acked-by: NMichal Privoznik <mprivozn@redhat.com>
Signed-off-by: NCole Robinson <crobinso@redhat.com>

docs/schemas/domaincaps.rng

@@ -142,12 +142,18 @@
 
   <define name='devices'>
     <element name='devices'>
-      <interleave>
+      <optional>
         <ref name='disk'/>
+      </optional>
+      <optional>
         <ref name='graphics'/>
+      </optional>
+      <optional>
         <ref name='video'/>
+      </optional>
+      <optional>
         <ref name='hostdev'/>
-      </interleave>
+      </optional>
     </element>
   </define>
 
@@ -181,12 +187,18 @@
 
   <define name='features'>
     <element name='features'>
-      <interleave>
+      <optional>
         <ref name='gic'/>
+      </optional>
+      <optional>
         <ref name='vmcoreinfo'/>
+      </optional>
+      <optional>
         <ref name='vmgenid'/>
+      </optional>
+      <optional>
         <ref name='sev'/>
-      </interleave>
+      </optional>
     </element>
   </define>