Scrub MdePkg:
- Add file description with doxygen format.
- Add calling convention of library class in MdePkg.
- Add function descriptions of public protocol/library class.
[Impaction]
It should be backward-compatible.
[Ref Info]
N/A
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@4985 6f19259b-4bc3-4df7-8a09-765794883524