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

Change-Id: I0fc966962413ee12f84058d702e7396e38460f27
diff --git a/src/cpu.c b/src/cpu.c
index 536fee1..a29c22d 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -19,10 +19,10 @@
 #include <stdalign.h>
 
 #include "hf/arch/cpu.h"
+#include "hf/arch/std.h"
 
 #include "hf/api.h"
 #include "hf/dlog.h"
-#include "hf/std.h"
 #include "hf/vm.h"
 
 #include "vmapi/hf/call.h"