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/arch/arm/mach-imx/mx6/litesom.c b/arch/arm/mach-imx/mx6/litesom.c
index 4f4df74..b0a6bd5 100644
--- a/arch/arm/mach-imx/mx6/litesom.c
+++ b/arch/arm/mach-imx/mx6/litesom.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2016 Grinn
  */
 
+#include <init.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/iomux.h>
 #include <asm/arch/imx-regs.h>