BaseTools: AutoGen refactor to iterate less

BaseTools: AutoGen refactor to iterate less

Don't iterate over new dictionaries with one item

Create the data and then add to dictionary.

Note: if you diff ignoring whitespace changes you
can more easily see the relevant changes.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@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>