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/test/openpower-pels/Makefile.include b/test/openpower-pels/Makefile.include
index 09eb36b..6ba7236 100644
--- a/test/openpower-pels/Makefile.include
+++ b/test/openpower-pels/Makefile.include
@@ -190,7 +190,8 @@
 	$(test_ldadd) \
 	$(top_builddir)/extensions/openpower-pels/failing_mtms.o \
 	$(top_builddir)/extensions/openpower-pels/json_utils.o \
-	$(top_builddir)/extensions/openpower-pels/mtms.o
+	$(top_builddir)/extensions/openpower-pels/mtms.o \
+	$(top_builddir)/extensions/openpower-pels/pel_values.o
 failing_mtms_test_LDFLAGS = $(test_ldflags)
 
 pel_values_test_SOURCES = %reldir%/pel_values_test.cpp