WhiskeylakeOpenBoardPkg: Update PCDs to enable stack sharing

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2409



Updated WhiskeylakeURvp PCDs to enable FSP/BL stack sharing.

This fixes the boot failure seen with the latest Coffee Lake (CFL)
FSP binary (v 7.0.68.41).

Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Co-authored-by: Michael Kubacki <michael.a.kubacki@intel.com>
Signed-off-by: Prince Agyeman <prince.agyeman@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>