tools/misc: xen-hvmcrash: New tool to attempt to crash HVM guests

tools/misc: xen-hvmcrash: New tool to attempt to crash HVM guests

This tool reads the CPU save records, overwrites RIP with a bogus
value, and then restores them. This is, of course, not guaranteed
to crash the guest (since the CPUs may not be executing in kernel
at the time) but it's good for breaking into some tight loops that
would be hard to debug otherwise.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>