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/samsung/arndale/arndale.c b/board/samsung/arndale/arndale.c
index 1d547b1..9abad3f 100644
--- a/board/samsung/arndale/arndale.c
+++ b/board/samsung/arndale/arndale.c
@@ -5,6 +5,7 @@
 
 #include <common.h>
 #include <cpu_func.h>
+#include <init.h>
 #include <usb.h>
 #include <asm/gpio.h>
 #include <asm/arch/pinmux.h>