Move std.c to arch to avoid conflicts with libc for tests.

Change-Id: I0fc966962413ee12f84058d702e7396e38460f27
diff --git a/src/fdt_handler.c b/src/fdt_handler.c
index f41fa8d..61b688d 100644
--- a/src/fdt_handler.c
+++ b/src/fdt_handler.c
@@ -16,13 +16,14 @@
 
 #include "hf/fdt_handler.h"
 
+#include "hf/arch/std.h"
+
 #include "hf/boot_params.h"
 #include "hf/cpu.h"
 #include "hf/dlog.h"
 #include "hf/fdt.h"
 #include "hf/layout.h"
 #include "hf/mm.h"
-#include "hf/std.h"
 
 static uint64_t convert_number(const char *data, uint32_t size)
 {