IntelFsp2Pkg: FSP Python scripts to support 3.x.

IntelFsp2Pkg: FSP Python scripts to support 3.x.

https://bugzilla.tianocore.org/show_bug.cgi?id=1930

Updated FSP Python scripts to support both 2.x and
3.x.

Test:
  . Verified with Python 2.7.12 and 3.6.6.
  . Verified tool result is the same before the change.
  . Both py -2 and py -3 built binary can boot.

Cc: Maurice Ma <maurice.ma@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>