AP_Logger: avoid logging dma.txt for normal builds

logging of dma.txt currently does no good as the first time you read
it you get no content. It then enables statistics in the shared_dma
code which makes all DMA operations slower, so all we are doing is
making DMA slower

libraries/AP_Logger/AP_Logger.cpp

@@ -1566,7 +1566,10 @@ void AP_Logger::prepare_at_arming_sys_file_logging()
      */
     static const char *log_content_filenames[] = {
         "@SYS/uarts.txt",
+#ifdef HAL_DEBUG_BUILD
+        // logging dma.txt has a performance impact
         "@SYS/dma.txt",
+#endif
         "@SYS/memory.txt",
         "@SYS/threads.txt",
         "@SYS/timers.txt",