guest: RISC-V virt guests support virtio-rng

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Andrea Bolognani <abologna@redhat.com>

tests/cli-test-xml/compare/virt-install-riscv64-graphics.xml

@@ -35,5 +35,8 @@
     <video>
       <model type="qxl"/>
     </video>
+    <rng model="virtio">
+      <backend model="random">/dev/urandom</backend>
+    </rng>
   </devices>
 </domain>

tests/cli-test-xml/compare/virt-install-riscv64-headless.xml

@@ -31,5 +31,8 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <rng model="virtio">
+      <backend model="random">/dev/urandom</backend>
+    </rng>
   </devices>
 </domain>

virtinst/guest.py

@@ -833,6 +833,7 @@ class Guest(XMLBuilder):
             return
         if not (self.os.is_x86() or
                 self.os.is_arm_machvirt() or
+                self.os.is_riscv_virt() or
                 self.os.is_s390x() or
                 self.os.is_pseries()):
             return