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/freescale/m5373evb/m5373evb.c b/board/freescale/m5373evb/m5373evb.c
index 37011fb..1d52ce0 100644
--- a/board/freescale/m5373evb/m5373evb.c
+++ b/board/freescale/m5373evb/m5373evb.c
@@ -9,6 +9,7 @@
 
 #include <config.h>
 #include <common.h>
+#include <init.h>
 #include <asm/immap.h>
 #include <asm/io.h>