MdeModulePkg: Replace UnicodeStrToAsciiStr/AsciiStrToUnicodeStr

MdeModulePkg: Replace UnicodeStrToAsciiStr/AsciiStrToUnicodeStr

It is the follow up of 3ab41b7a325ca11a12b42f5ad1661c4b6791cb49
to replace UnicodeStrToAsciiStr/AsciiStrToUnicodeStr with
UnicodeStrToAsciiStrS/AsciiStrToUnicodeStrS.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>