Move headers under the hf directory.

This helps distinguish local headers from the more official headers.

Change-Id: I535c1b44081b9d60ba63666cd1ad514aaaf2c68d
diff --git a/src/fdt.c b/src/fdt.c
index faf42b3..6383164 100644
--- a/src/fdt.c
+++ b/src/fdt.c
@@ -1,9 +1,9 @@
-#include "fdt.h"
+#include "hf/fdt.h"
 
 #include <stdint.h>
 
-#include "dlog.h"
-#include "std.h"
+#include "hf/dlog.h"
+#include "hf/std.h"
 
 struct fdt_header {
 	uint32_t magic;