BaseTools: Regular Expressions refactor out the hex char for later reuse

BaseTools: Regular Expressions refactor out the hex char for later reuse

move hex character info from GUID expressions into seperate variable to
facilitate reuse.

I had a type with insufficient {} in the first version.

Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>