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/ronetix/pm9263/pm9263.c b/board/ronetix/pm9263/pm9263.c
index 2da39c4..3cd6384 100644
--- a/board/ronetix/pm9263/pm9263.c
+++ b/board/ronetix/pm9263/pm9263.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <linux/sizes.h>
 #include <asm/io.h>
 #include <asm/gpio.h>