Per PI spec, StatusCode related structure is not required to be defined as packed...

Per PI spec, StatusCode related structure is not required to be defined as packed byte. So, StatusCode related structures are updated from packed to unpacked.
Notes:
1. This patch is an incompatible change for the binary image built based on previous EDKII code. But, it is a compatible change for source.
2. This change will make StatusCode related definition in MdePkg to align the one defined in EcpPkg. Then, EDK driver based on EcpPkg can work together EDKII core.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11316 6f19259b-4bc3-4df7-8a09-765794883524