memory: Let ReservedRegion use Range

memory: Let ReservedRegion use Range

A reserved region is a range tagged with a type. Let's directly use
the Range type in the prospect to reuse some of the library helpers
shipped with the Range type.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>