Add host cache information in capabilities

Add host cache information in capabilities

We're only adding only info about L3 caches, we can add more
later (just by changing one line), but for now that's more than enough
without overwhelming anyone.

XML snippet of how this should look like (also seen as part of the commit):

  <cache>
    <bank id='0' level='3' type='both' size='8192' unit='KiB' cpus='0-7'/>
  </cache>

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>