Add Post code description

Added functionality to read post code description from post_desc.json
file stored in /usr/share/ipmi-providers/. This file is platform
specific and can be overwritten for different platforms. This
post code description will be requested by lcd debug card for
displaying in screen.

Tested: verified with lcd debug card screen.

Change-Id: I655178fd031cf7107a04db1f587ae35a1bc9d4d8
Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
4 files changed