Don't save Xen heap pages during domain save

Don't save Xen heap pages during domain save

As discussed in the thread starting at
http://lists.xensource.com/archives/html/xen-devel/2010-05/msg01383.html,
don't save Xen heap pages in order to avoid overallocation when the
domain gets restored, as those pages would get (temporarily) backed
with normal RAM pages by the restore code.

This requires making DOMCTL_getpageframeinfo{2,3} usable for HVM
guests, meaning that the input to these must be treated as GMFNs.

Signed-off-by: Jan Beulich <jbeulich@novell.com>