vhost-vdpa: Remove redundant declaration of address_space_memory

vhost-vdpa: Remove redundant declaration of address_space_memory

The symbol address_space_memory are already declared in
include/exec/address-spaces.h. So let's add this header file
and remove the redundant declaration in include/hw/virtio/vhost-vdpa.h.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20210517123246.999-1-xieyongji@bytedance.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>