common: Move RAM-sizing functions to init.h

These functions relate to memory init so move them into the init
header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/egnite/ethernut5/ethernut5.c b/board/egnite/ethernut5/ethernut5.c
index 9dea2ba..bfd5a4f 100644
--- a/board/egnite/ethernut5/ethernut5.c
+++ b/board/egnite/ethernut5/ethernut5.c
@@ -53,6 +53,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <net.h>
 #include <netdev.h>
 #include <miiphy.h>