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/templates/errors.mako.hpp b/src/templates/errors.mako.hpp
new file mode 100644
index 0000000..e28d9f9
--- /dev/null
+++ b/src/templates/errors.mako.hpp
@@ -0,0 +1 @@
+#include "${c.error.split('Error::', 1)[0].replace('::','/')}error.hpp"