IntelFsp2Pkg: Fix FSP binary rebasing issue for PE32+ image

IntelFsp2Pkg: Fix FSP binary rebasing issue for PE32+ image

Current FSP rebasing script SplitFspBin.py has support for both
PE32 and PE32+ image formats. However, while updating the ImageBase
field in the image header, it always assumed the ImageBase field is
32bit long. Since PE32+ image format defined ImageBase as 64bit,
the current script will only update the lower 32bit value and leave
the upper 32bit untouched. It does not work well for PE32+ image
that requires update in the upper 32bit ImageBase field. The
expected behavior is to update the full 64bit field. This patch
implemented this fix.

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