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/x86/cpu/tangier/sdram.c b/arch/x86/cpu/tangier/sdram.c
index b47d896..8c7e1c1 100644
--- a/arch/x86/cpu/tangier/sdram.c
+++ b/arch/x86/cpu/tangier/sdram.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <asm/e820.h>
 #include <asm/global_data.h>
 #include <asm/sfi.h>