Read CPU IDs from FDT in tests, so they work under FVP.

Bug: 117551008
Change-Id: I14e24e86631f9e7c16ad69decf676b343ac9f252
diff --git a/test/hftest/inc/hftest.h b/test/hftest/inc/hftest.h
index d22cadf..bcffe5c 100644
--- a/test/hftest/inc/hftest.h
+++ b/test/hftest/inc/hftest.h
@@ -90,5 +90,7 @@
  */
 #define HFTEST_LOG_INDENT "    "
 
+uintptr_t hftest_get_cpu_id(size_t index);
+
 /* Above this point is the public API. Now include the implementation. */
 #include <hftest_impl.h>