mem: Populate the secure flag in the writeback visitor

Previously the writeback visitor would not consider and set the secure
flag for the blocks that are written back to memory. This patch fixes
this.

Change-Id: Ie1a425fa9211407a70a4343f2c6b3d073371378f
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>

src/mem/cache/cache.cc

@@ -1636,6 +1636,9 @@ Cache::writebackVisitor(CacheBlk &blk)
         Request request(tags->regenerateBlkAddr(blk.tag, blk.set),
                         blkSize, 0, Request::funcMasterId);
         request.taskId(blk.task_id);
+        if (blk.isSecure()) {
+            request.setFlags(Request::SECURE);
+        }
 
         Packet packet(&request, MemCmd::WriteReq);
         packet.dataStatic(blk.data);