BaseTools: AutoGen - tag a function as cachable
BaseTools: AutoGen - tag a function as cachable

MakeFile generation is once per module, so mark it as such.
also move the time stamp creation function inside as it's
only called from one place.

Cc: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Cc: Yonghong Zhu <78d981fe33a016071af5222c56d5cf77f30fb0b2@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jaben Carsey <2d4ee76b36e91bee3a58378b7538904eb027a616@intel.com>
Reviewed-by: Yonghong Zhu <78d981fe33a016071af5222c56d5cf77f30fb0b2@intel.com>

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2