Framework code may call PreparePacckage with NULL GUID and both IFR and String Packages.

Framework code may call PreparePacckage with NULL GUID and both IFR and String Packages.
    PackageList = PreparePackages (2, NULL, IfrPack, StringPack);

    mHii->NewPack( mHii, PackageList, &HiiHandle );

Framework HII database make use of the formset GUID as ID to retrieve String using

EFI_STATUS
GetStringFromToken (
  IN  EFI_GUID                  *ProducerGuid,
  IN  STRING_REF                Token,
  OUT CHAR16                    **String
  )

Update the code to cache the Formset GUID too.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@5896 6f19259b-4bc3-4df7-8a09-765794883524