MdeModulePkg: Misc comments and DEBUG messages

Fixed some spelling typos in some comments. Added a couple of useful DEBUG messages 

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Samer El-Haj-Mahmoud <samer.el-haj-mahmoud@hp.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16450 6f19259b-4bc3-4df7-8a09-765794883524