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/woodburn/woodburn.c b/board/woodburn/woodburn.c
index 5cab3f4..c69df6c 100644
--- a/board/woodburn/woodburn.c
+++ b/board/woodburn/woodburn.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <asm/io.h>
 #include <linux/errno.h>
 #include <asm/arch/imx-regs.h>