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/drivers/ddr/altera/sdram_gen5.c b/drivers/ddr/altera/sdram_gen5.c
index 435f42b..a3b914f 100644
--- a/drivers/ddr/altera/sdram_gen5.c
+++ b/drivers/ddr/altera/sdram_gen5.c
@@ -6,6 +6,7 @@
 #include <dm.h>
 #include <errno.h>
 #include <div64.h>
+#include <init.h>
 #include <ram.h>
 #include <reset.h>
 #include <watchdog.h>