PEL: Add function to get PEL size

Add a size() function to the PEL class that adds up the size fields
in the header of every PEL section.

This required a fix to some testcases where the size field was wrong in
a header.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I0d70deae116cd3835f2c0ab34e13811da471fb14
diff --git a/test/openpower-pels/real_pel_test.cpp b/test/openpower-pels/real_pel_test.cpp
index 1846239..a170812 100644
--- a/test/openpower-pels/real_pel_test.cpp
+++ b/test/openpower-pels/real_pel_test.cpp
@@ -548,6 +548,7 @@
     // Check that the flat data is correct
     auto flat = pel.data();
     EXPECT_EQ(realPELData, flat);
+    EXPECT_EQ(realPELData.size(), pel.size());
 
     // Check that the code can extract an object for every section.
     //(The PrivateHeader and UserHeader account for the + 2 below.)