Move headers under the hf directory.

This helps distinguish local headers from the more official headers.

Change-Id: I535c1b44081b9d60ba63666cd1ad514aaaf2c68d
diff --git a/src/vm.c b/src/vm.c
index 1eafb63..963531a 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1,8 +1,8 @@
-#include "vm.h"
+#include "hf/vm.h"
 
-#include "api.h"
-#include "cpu.h"
-#include "std.h"
+#include "hf/api.h"
+#include "hf/cpu.h"
+#include "hf/std.h"
 
 bool vm_init(struct vm *vm, uint32_t id, uint32_t vcpu_count)
 {