This patch is to align the code behavior with UNI spec that string token
identifier can use upper case and lower case letters.
Cc: Liming Gao <liming.gao@intel.com>
Cc: Felix <Felixp@ami.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>