UefiPayloadPkg: Enhance build script for BuildEntryOnly

Currently, have two command for pre-build binary support
1. --BuildEntryOnly: build UPL Entry file
2. --PreBuildUplBinary: build UPL binary based on UPL

And these two commands should be exclusived, shouldn't
have chance run it in the meantime.

Case1: Build UPL entry with CLANGDWARF
  python UefiPayloadPkg/UniversalPayloadBuild.py --BuildEntryOnly

Case2: Use pre-built UPL entry and build other fv by VS2019
  python UefiPayloadPkg/UniversalPayloadBuild.py -t VS2019 \
    --PreBuildUplBinary UniversalPayload.elf

Case3: Build UPL Entry with CLANGDWARF and build other fv by VS2019
  python UefiPayloadPkg/UniversalPayloadBuild.py -t VS2019

Cc: Guo Dong <guo.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Sean Rhodes <sean@starlabs.systems>
Cc: James Lu <james.lu@intel.com>
Cc: Gua Guo <gua.guo@intel.com>
Signed-off-by: Gua Guo <gua.guo@intel.com>
Reviewed-by: James Lu <james.lu@intel.com>