Static layout: support image verification

Add support of image verification for static layout PNOR code update.

Tested: Verify the PNOR code update succeeds with valid-signed PNOR;
        and fails with invalid-signed PNOR or a PNOR tarball without
        signature.

Change-Id: I1aafeb4e8e07eaa16c170f33f4f21940f7c9c146
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/static/activation_static.hpp b/static/activation_static.hpp
index 6fe7138..258a612 100644
--- a/static/activation_static.hpp
+++ b/static/activation_static.hpp
@@ -2,6 +2,8 @@
 
 #include "activation.hpp"
 
+#include <filesystem>
+
 namespace openpower
 {
 namespace software
@@ -9,6 +11,8 @@
 namespace updater
 {
 
+namespace fs = std::filesystem;
+
 /** @class ActivationStatic
  *  @brief Implementation for static PNOR layout
  */
@@ -25,6 +29,8 @@
     void finishActivation() override;
 
     std::string pnorUpdateUnit;
+
+    fs::path pnorFilePath;
 };
 
 } // namespace updater