X86/vMCE: handle broken page with regard to migration

X86/vMCE: handle broken page with regard to migration

At the sender
  xc_domain_save has a key point: 'to query the types of all the pages
  with xc_get_pfn_type_batch'
  1) if broken page occur before the key point, migration will be fine
     since proper pfn_type and pfn number will be transferred to the
     target and then take appropriate action;
  2) if broken page occur after the key point, whole system will crash
     and no need care migration any more;

At the target
  Target will populates pages for guest. As for the case of broken page,
  we prefer to keep the type of the page for the sake of seamless migration.
  Target will set p2m as p2m_ram_broken for broken page. If guest access
  the broken page again it will kill itself as expected.

Suggested-by: George Dunlap <george.dunlap@eu.citrix.com>
Signed-off-by: Liu Jinsong <jinsong.liu@intel.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Ian Campbell <ian.campbell@citrix.com>