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/imx8/cpu.c b/arch/arm/mach-imx/imx8/cpu.c
index d31af47..2110380 100644
--- a/arch/arm/mach-imx/imx8/cpu.c
+++ b/arch/arm/mach-imx/imx8/cpu.c
@@ -8,6 +8,7 @@
 #include <cpu.h>
 #include <cpu_func.h>
 #include <dm.h>
+#include <init.h>
 #include <dm/device-internal.h>
 #include <dm/lists.h>
 #include <dm/uclass.h>