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

Change-Id: I0fc966962413ee12f84058d702e7396e38460f27
diff --git a/src/api.c b/src/api.c
index ba89203..a155bb6 100644
--- a/src/api.c
+++ b/src/api.c
@@ -19,12 +19,12 @@
 #include <assert.h>
 
 #include "hf/arch/cpu.h"
+#include "hf/arch/std.h"
 #include "hf/arch/timer.h"
 
 #include "hf/dlog.h"
 #include "hf/mm.h"
 #include "hf/spinlock.h"
-#include "hf/std.h"
 #include "hf/vm.h"
 
 #include "vmapi/hf/call.h"