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>