OvmfPkg: Prepare OvmfPkg to use the VmgExitLib library
    
    BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
    
    Various CpuExceptionHandlerLib libraries will updated to use the new
    VmgExitLib library. To prevent any build breakage, update the OvmfPkg
    DSC files that use a form of the CpuExceptionHandlerLib library to
    include the VmgExitLib library.
    
    Cc: Jordan Justen <jordan.l.justen@intel.com>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
    Cc: Anthony Perard <anthony.perard@citrix.com>
    Cc: Julien Grall <julien@xen.org>
    Reviewed-by: Laszlo Ersek <lersek@redhat.com>
    Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    Regression-tested-by: Laszlo Ersek <lersek@redhat.com>