FitGen: Update tool to meet FIT specification revision 1.2

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2687



  FIT specification revision 1.2 was released to the open community.
  Revision 1.2 updates CSE Secure Boot Rules (section 4.12) and adds
  2 new entry sub-types used to distinguish the CSE entries.

Signed-off-by: Jorge Hernandez Beltran <jorge.hernandez.beltran@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>