Add new spice-module.c + qemu-spice-module.h files.  The code needed to
support modular spice will be there.  For starters this will be only the
using_spice variable, more will follow ...

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20201019075224.14803-2-kraxel@redhat.com