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/common/memsize.c b/common/memsize.c
index 13b0047..e95c682 100644
--- a/common/memsize.c
+++ b/common/memsize.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 
 DECLARE_GLOBAL_DATA_PTR;