BaseTools/GenFw: add new option to not zero PE/COFF optional header fields

BaseTools/GenFw: add new option to not zero PE/COFF optional header fields

Add new option --keepoptionalheader and that flag does not zero PE/COFF
optional header fields including the version fields. It can support the
case that the PE/COFF optional header would be kept.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18767 6f19259b-4bc3-4df7-8a09-765794883524