1. Add two performance measurement points for SMM performance measurement;

1. Add two performance measurement points for SMM performance measurement;
2. Introduce SmmCorePlatformHookLib library class defining two platform hook points. Update PI Smm Core to call the hook points before and after invoking registered SMI handlers. A NULL instance of this library class is implemented.

Note that after this check in, DSC files consuming the PiSmmCore.inf need to be updated to add a library instance for SmmCorePlatformHookLib library class.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12140 6f19259b-4bc3-4df7-8a09-765794883524