The SST NV counter tests call sst_system_prepare() directly, which causes a problem when SST code makes requests to other partitions, as the request will come from the TF-M test partition instead of SST. To work around this, call sst_system_prepare() from an SST test partition instead. This will make it possible for other partitions to determine when requests are coming from SST tests directly calling SST code, in test builds.