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/freescale/mx53smd/mx53smd.c b/board/freescale/mx53smd/mx53smd.c
index cab0e79..2599272 100644
--- a/board/freescale/mx53smd/mx53smd.c
+++ b/board/freescale/mx53smd/mx53smd.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <asm/io.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/sys_proto.h>