Add PcdRtcDefaultYear to specify the default year to use when the RTC is in an invalid state. Make sure PcdRtcDefaultYear is >= PcdMinimalValidYear and <= PcdMaximalValidYear. Set the default value for this PCD to PcdMinimalValidYear to preserve the existing behavior. A platform DSC file can override this default value setting. Cc: Ray Ni <ray.ni@intel.com> Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com> Reviewed-by: Ray Ni <ray.ni@intel.com>