conf: Add keyboard input device type

There is no keyboard support currently in libvirt.

For some platforms (PPC64 QEMU) this makes graphics unusable,
since the keyboard is not implicit and it can't be added via libvirt.

Signed-off-by: Li Zhang <zhlcindy@linux.vnet.ibm.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>

tests/vmx2xmldata/vmx2xml-graphics-vnc.xml

@@ -12,6 +12,7 @@
   <on_crash>destroy</on_crash>
   <devices>
     <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
     <graphics type='vnc' port='5903' autoport='no' keymap='de' passwd='password'/>
     <video>
       <model type='vmvga' vram='4096'/>