Add support for elog callback

Added support for "callback: elog" in PDM.
templates/elog.mako.cpp is used to generate the Elog call.
templates/errors.mako.hpp is used to generate the errors.hpp
used by generated.hpp to include any error.hpp files like
"xyz/openbmc_project/Common/error.hpp"

Change-Id: Id0ae3aca4282095f58a8939b70e398bec706d7f5
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/src/Makefile.am b/src/Makefile.am
index 211cb9f..c6a041f 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -29,6 +29,7 @@
 	templates/generated.mako.hpp \
 	templates/journal.mako.cpp \
 	templates/elog.mako.cpp \
+	templates/errors.mako.hpp \
 	templates/method.mako.cpp
 
 generated.hpp: $(PDMGEN) $(YAML_PATH) $(TEMPLATES)