To be able to factor out address assignment of memory devices, we will
have to read (get_addr()) and write (set_addr()) the address.

We can't use properties for this purpose, as properties are device
specific. E.g. while the address property for a DIMM is called "addr", it
might be called differently (e.g. "memaddr") for other devices.

Especially virtio based memory devices cannot use "addr" as that is already
reserved and used for the address on the bus (for the proxy device).

Also, it might be possible to have memory devices without address
properties (e.g. internal DIMM-like thingies).

In contrast to get_addr(), we expect that set_addr() can fail.

Keep it simple for now for pc-dimm and simply set the static property, that
will fail once realized.
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NEric Auger <eric.auger@redhat.com>
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Message-Id: <20181005092024.14344-13-david@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>