Fix ECC errors:1.Update the comments in function headers to follow the Doxygen specia...

Fix ECC errors:1.Update the comments in function headers to follow the Doxygen special documentation. 2.Make the first line of text in  a comment block end with a period. 3.Update the member variable name for SHELL_OPERATION_TYPES to follow the rules "Must contain lower case characters". 4. Return type of a function should exist and in the first line.

Signed-off-by: Shumin Qiu <shumin.qiu@intel.com>
Reviewed-by: Dong, Eric <eric.dong@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15019 6f19259b-4bc3-4df7-8a09-765794883524