QOMify memory regions as an Object. The former init() and destroy()
routines become instance_init() and instance_finalize() resp.
memory_region_init() is re-implemented to be:
object_initialize() + set fields
memory_region_destroy() is re-implemented to call unparent().
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
[Add newly-created MR as child, unparent on destruction. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>