Add repo specific errors

1. Add Internal.errors.yaml to define repo specific errors
2. Update configure.ac and Makefile.am to generate code from error yamls
3. Add elog-gen.hpp generated by elog-gen.py

Change-Id: I6858f2c9f3c2100ce106d1effe7ad3f340117fec
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/.gitignore b/.gitignore
index 5cde092..256b418 100644
--- a/.gitignore
+++ b/.gitignore
@@ -48,6 +48,7 @@
 phosphor-timemanager
 *-libtool
 .libs
+/xyz/openbmc_project/Time/Internal/*
 
 # UT related items
 .dirstamp