Recently CPU hardware vendors have started to support a new structure
inside the CPU package topology known as a "die". Thus the hierarchy
is now:

  sockets > dies > cores > threads

This adds support for "dies" in the XML parser, with the value
defaulting to 1 if not specified for backwards compatibility.

For example a system with 64 logical CPUs might report

   <topology sockets="4" dies="2" cores="4" threads="2"/>
Reviewed-by: NJiri Denemark <jdenemar@redhat.com>
Reviewed-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>