made sd code only compile with SDSUPPORT defined. safes 10k of codespace

Marlin/SdFile.cpp

@@ -18,6 +18,8 @@
  * <http://www.gnu.org/licenses/>.
  */
 #include "Marlin.h"
+
+#ifdef SDSUPPORT
 #include "SdFile.h"
 /**  Create a file object and open it in the current working directory.
  *
@@ -85,3 +87,6 @@ void SdFile::writeln_P(PGM_P str) {
   write_P(str);
   write_P(PSTR("\r\n"));
 }
+
+
+#endif