BaseTools: Enhance parse performance by optimize ValueExpressionEx

BaseTools: Enhance parse performance by optimize ValueExpressionEx

Optimize ValueExpressionEx function to enhance meta-data file parse
performance.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yunhua Feng <yunhuax.feng@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>