PEL: Add PrivateHeader class

The first section in a PEL is always the 'Private Header' section.  This
commit adds a class to represent that.  Right now, the only constructor
available is filling in its data fields from a PEL stream.

The Section base class, which will be the base class of all PEL
sections, is also being introduced here.  It contains the section header
structure, and a valid flag that derived classes can use.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Ia5806017155fe1ef29ea57bf8ab202ff861bde2e
diff --git a/extensions/openpower-pels/openpower-pels.mk b/extensions/openpower-pels/openpower-pels.mk
index 94c7bb8..8a852d4 100644
--- a/extensions/openpower-pels/openpower-pels.mk
+++ b/extensions/openpower-pels/openpower-pels.mk
@@ -1,5 +1,5 @@
 phosphor_log_manager_SOURCES += \
 	extensions/openpower-pels/bcd_time.cpp \
 	extensions/openpower-pels/entry_points.cpp \
-	extensions/openpower-pels/manager.cpp
-
+	extensions/openpower-pels/manager.cpp \
+	extensions/openpower-pels/private_header.cpp