PEL: peltool: Add const strings for section header

Added "Section Version", "Sub-section type" and "Created by" constant strings.

Updated all getJSON() functions to use the new constants.

Signed-off-by: Harisuddin Mohamed Isa <harisuddin@gmail.com>
Change-Id: I434192afed929972845c3cfb8876cc5ef784eec2
diff --git a/extensions/openpower-pels/pel_values.hpp b/extensions/openpower-pels/pel_values.hpp
index 2424c63..d7d4226 100644
--- a/extensions/openpower-pels/pel_values.hpp
+++ b/extensions/openpower-pels/pel_values.hpp
@@ -26,6 +26,10 @@
 using PELFieldValue = std::tuple<uint32_t, const char*, const char*>;
 using PELValues = std::vector<PELFieldValue>;
 
+const std::string sectionVer = "Section Version";
+const std::string subSection = "Sub-section type";
+const std::string createdBy = "Created by";
+
 /**
  * @brief Helper function to get values from lookup tables.
  * @return std::string - the value