pv-on-hvm: Signal crash to Xen tools when HVM guest panics.

pv-on-hvm: Signal crash to Xen tools when HVM guest panics.

Attached patch adds a function to automatically dump core file when
guest linux on HVM domain panics, in the same way as PV domain.

I tested this patch with kernel 2.6.9 and 2.6.18 on both of x86 and
ia64 (to buid for ia64, some patches in the ia64 tree are needed) by
the following steps, and confirmed it works well:

1. Build xen-platform-pci.ko.
2. In /etc/xen/xend-config.sxp, set (enable-dump yes).
3. On guest linux, execute insmod:
   # insmod xen-platform-pci.ko
4. When guest linux panics, a core file is dumped.

Signed-off-by: Tetsu Yamamoto <yamamoto.tetsu@jp.fujitsu.com>