MdeModulePkg: Change TCG MOR variables to use VariablePolicy

MdeModulePkg: Change TCG MOR variables to use VariablePolicy

https://bugzilla.tianocore.org/show_bug.cgi?id=2522

These were previously using VarLock, which is
being deprecated.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Bret Barkelew <brbarkel@microsoft.com>
Signed-off-by: Bret Barkelew <brbarkel@microsoft.com>
Reviewed-by: Dandan Bi <dandan.bi@intel.com>
Acked-by: Jian J Wang <jian.j.wang@intel.com>