libxc: Support cross-bitness guest when core-dumping

libxc: Support cross-bitness guest when core-dumping

This patch allows core-dumping to work on a cross-bit host/guest
configuration, whereas previously that was not supported.  It supports
both PV and FV guests. The core file format generated by the host,
needs to match that of the guest, so an alignment issue is addressed,
along with the p2m frame list handling being done according to the
guest size.

Signed-off-by: Bruce Rogers <brogers@novell.com>