PEL: Add missing include

Compiles done with newer versions of yocto will fail otherwise.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I16c967a90a9120652189dad6615bcbd363dca0af
diff --git a/extensions/openpower-pels/fru_identity.hpp b/extensions/openpower-pels/fru_identity.hpp
index e911b13..bcb2956 100644
--- a/extensions/openpower-pels/fru_identity.hpp
+++ b/extensions/openpower-pels/fru_identity.hpp
@@ -3,6 +3,7 @@
 #include "pel_types.hpp"
 #include "stream.hpp"
 
+#include <array>
 #include <optional>
 
 namespace openpower