WhitleyOpenBoardPkg: Use CcExitLib instead of VmgExitLib

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4159



VmgExitLib is renamed as CcExitLib in EDK2. This change should be
applied in WhitleyOpenBoardPkg as well.

Cc: Isaac Oram <isaac.w.oram@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>