frup: add missing header

Add missing header "utility" provides std::pair<>.

Change-Id: I5d303c5f41f7af16ef3dc75fdd9818ed17978a5a
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/frup.hpp b/frup.hpp
index 0a0dd76..6afd621 100644
--- a/frup.hpp
+++ b/frup.hpp
@@ -6,6 +6,7 @@
 #include <array>
 #include <map>
 #include <string>
+#include <utility>
 #include <vector>
 
 enum ipmi_fru_area_type