The NBA's Christmas Day tip-off schedule is taking shape.  Three games were originally scheduled for December 25th, the target date for the start of the 2011-12 season.  According to multiple reports the NBA will add two more games, bringing the total to five.  The Celtics were originally set to play the Knicks, the Heat and Mavericks were lined up to rematch last year's NBA Finals and the Lakers were prepared to face the Bulls.  The DailyThunder.com reports Oklahoma City will play host to a Christmas evening game.  The opponent remains a mystery, but the Grizzlies and Magic are rumored to be in the mix.  According to the "Contra Costa Times," the Warriors and Clippers will play the fifth and final game of the day.