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/mips/mach-ath79/dram.c b/arch/mips/mach-ath79/dram.c
index 138a7f8..1abe2a4 100644
--- a/arch/mips/mach-ath79/dram.c
+++ b/arch/mips/mach-ath79/dram.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <linux/sizes.h>
 #include <asm/addrspace.h>
 #include <mach/ddr.h>