BaseTools: Fix re-build issue after tools_def/build_rule updated.

Add tools_def.txt and build_rule.txt to workspace autogen timestamp file.
Now it will not skip autogen if this two file is updated.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Derek Lin <derek.lin2@hpe.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>