BOSTON — The cheering was as advertised when the Celtics stepped onto the parquet Monday night for pregame warmups, none of it directed at any one player. Not yet. But then Derrick White appeared on the flat screens that are suspended high above center court at TD Garden, and suddenly the cheering got even louder, so loud that White looked around to see what the fuss was all about. Advertisement Looking up, he smiled in a way that suggested he might have been saying … Oh, you’re cheering me. Cool. And that’s the way it’s going to be for the…