memory: MemoryRegion: Add container and addr props

Expose the already existing .parent and .addr fields as QOM properties.
.parent (i.e. the field describing the memory region that contains this
one in Memory hierachy) is renamed "container". This is to avoid
confusion with the QOM parent.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
[Remove setters.  Do not unref parent on releasing the property. Clean
 up error propagation. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
