Don't share privregs with hvm domain and twist IA64 xen dump core format slightly. Xen shares privregs pages with IA64 HVM domain for xm dump-core to dump the pages. However sharing the page allows hvm guest domain peek/destroy the page contents that might cause xen crash. And the xen dump core file doesn't need privregs page because cpu context should be obtained from vcpu context in case of IA64 HVM domain.

Although this patch modify xen dump core format, current crash utility (at least crash 4.0-4.7) doesn't look into .xen_ia64_mmapped_regs section and I don't know any other tools to understand xen dump core file. So this format modification doesn't cause incompatibility issue.