x86/mm: Check how many mfns are shared, in addition to how many are saved

x86/mm: Check how many mfns are shared, in addition to how many are saved

This patch also moves the existing sharing-related memory op to the
correct location, and adds logic to the audit() method that uses the
new information.

This patch only provides the Xen implementation of the domctls.

Signed-off-by: Andres Lagar-Cavilla <andres@scannell.ca>
Signed-off-by: Adin Scannell <adin@scannell.ca>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>