common: Move testdram() into init.h

This function is called during init so move it to the init header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/sysam/stmark2/stmark2.c b/board/sysam/stmark2/stmark2.c
index 790199a..ce8b541 100644
--- a/board/sysam/stmark2/stmark2.c
+++ b/board/sysam/stmark2/stmark2.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <spi.h>
 #include <asm/io.h>
 #include <asm/immap.h>