BaseTool: Support different PCDs that refers to the same EFI variable.
BaseTool: Support different PCDs that refers to the same EFI variable.

V2:
Make the code of patch both compatible for Python2 and Python3.

V1:
If different PCDs refer to the same EFI variable, then do EFI variable
combination, according to the VariableOffset of different PCDS.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: ZhiqiangX Zhao <d5cb37baecf82d4076c20e2d5029706f03fe31a0@intel.com>
Cc: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Cc: Yonghong Zhu <78d981fe33a016071af5222c56d5cf77f30fb0b2@intel.com>
Cc: Bob Feng <f53a8c5610dbb66123cb988c78ae464e9da7199c@intel.com>
Reviewed-by: Bob Feng <f53a8c5610dbb66123cb988c78ae464e9da7199c@intel.com>

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