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-meson/board-g12a.c b/arch/arm/mach-meson/board-g12a.c
index 24786df..26d6b90 100644
--- a/arch/arm/mach-meson/board-g12a.c
+++ b/arch/arm/mach-meson/board-g12a.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <asm/arch/boot.h>
 #include <asm/arch/eth.h>
 #include <asm/arch/g12a.h>